The 2009 swine flu pandemic, caused by the
H1N1 influenza virus and declared by the
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920
Spanish flu
The 1918–1920 influenza pandemic, commonly known by the misnomer Spanish flu or as the Great Influenza epidemic, was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was ...
pandemic and the second being the
1977 Russian flu
The 1977 Russian flu was an influenza pandemic that was first reported by the Soviet Union in 1977 and lasted until 1979. The outbreak in northern China started in May 1977, slightly earlier than that in the Soviet Union. The pandemic mostly affe ...
).
The first two cases were discovered independently in the United States in April 2009.
The virus appeared to be a new strain of H1N1 that resulted from a previous triple
reassortment
Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and chromosomal crossover. It is particula ...
of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "
swine flu
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As o ...
".
Some studies estimated that the real number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of the global population of 6.8 billion at the time.
The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic.
However, the Spanish flu infected approximately a third of the world population at the time, a much higher proportion.
The number of lab-confirmed deaths reported to the WHO is 18,449
and is widely considered a gross underestimate. The WHO collaborated with the
US Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
(USCDC) and Netherlands Institute for Health Services Research (NIVEL) to produce two independent estimates of the influenza deaths that occurred during the global pandemic using two distinct methodologies. The 2009 H1N1 flu pandemic is estimated to have actually caused about 284,000 (range from 150,000 to 575,000) excess deaths by the WHO-USCDC study and 148,000–249,000 excess respiratory deaths by the WHO-NIVEL study.
A study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly
seasonal flu
Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemisphere. It takes approximately two days to show symptoms. Influen ...
. For comparison, the WHO estimates that 250,000 to 500,000 people die of seasonal flu annually.
However, the H1N1 influenza epidemic in 2009 resulted in a large increase in the number of new cases of
narcolepsy
Narcolepsy is a long-term neurological disorder that involves a decreased ability to regulate sleep–wake cycles. Symptoms often include periods of excessive daytime sleepiness and brief involuntary sleep episodes. About 70% of those affec ...
.
Unlike most strains of influenza, the
pandemic H1N1/09 virus
The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media. For other names, see the Nomenclature section ...
did not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1
pandemic
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...
. Even in the case of previously healthy people, a small percentage develop
pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
or
acute respiratory distress syndrome
Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin colo ...
(ARDS). This manifests itself as increased breathing difficulty and typically occurs three to six days after initial onset of flu symptoms.
The pneumonia caused by flu can be either direct
viral pneumonia
Viral pneumonia is a pneumonia caused by a virus. Pneumonia is an infection that causes inflammation in one or both of the lungs. The pulmonary alveoli fill with fluid or pus making it difficult to breathe. Pneumonia can be caused by bacteria, vir ...
or a secondary
bacterial pneumonia
Bacterial pneumonia is a type of pneumonia caused by bacterial infection.
Types
Gram-positive
''Streptococcus pneumoniae'' () is the most common bacterial cause of pneumonia in all age groups except newborn infants. ''Streptococcus pneumoniae'' ...
. A November 2009 ''
New England Journal of Medicine
''The New England Journal of Medicine'' (''NEJM'') is a weekly medical journal published by the Massachusetts Medical Society. It is among the most prestigious peer-reviewed medical journals as well as the oldest continuously published one.
Hist ...
'' article recommended that flu patients whose
chest X-ray
A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...
indicates pneumonia receive both
antiviral
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...
s and
antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
s. In particular, it is a warning sign if a child seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia.
[
]
Name
The World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
uses the term "(H1N1) 2009 pandemic" when referring to the event, and officially adopted the name "A(H1N1)pdm09" for the virus in 2010, after the conclusion of the pandemic.
Controversy arose early on regarding the wide assortment of terms used by journalists, academics,
and officials. Labels like "H1N1 flu", "Swine flu", "Mexican flu", and variations thereof were typical. Criticism centered on how these names may confuse or mislead the public. It was argued that the names were overly technical (e.g. "H1N1"), incorrectly implying that the disease is caused by contact with pigs
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
or pig products, or provoking stigmatization against certain communities (e.g. "Mexican"). Some academics of the time asserted there is nothing wrong with such names, while research published years later (in 2013) concluded that Mexican Americans and Latino Americans had indeed been stigmatized due to the frequent use of term "Mexican flu" in the news media.
Official entities adopted terms with varying consistency over the course of the pandemic. The CDC
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
used names like "novel influenza A (H1N1)" or "2009 H1N1 flu". The used the term "Pig Flu" early on. Officials in Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
suggested use of the names "H1N1 flu" or "new flu". The World Organization for Animal Health
The World Organisation for Animal Health (WOAH), formerly the (OIE), is an intergovernmental organization coordinating, supporting and promoting animal disease control.
Mission and status
The main objective of the WOAH is to control epizoo ...
, an IGO based in Europe, proposed the name "North American influenza". The European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
adopted the term "novel flu virus". Officials in Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
and South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
briefly considered adoption of the name "Mexican virus" due to concern about the use of the word "swine". In Israel, objections stemmed from sensitivity to religious restrictions on eating pork in the Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
and Muslim
Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...
populations, in South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
, concerns were influenced by the importance of pork
Pork is the culinary name for the meat of the domestic pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BCE.
Pork is eaten both freshly cooked and preserved; ...
and domestic pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
s.
As terminology changed to deal with these and other such issues, further criticism was made that the situation was unnecessarily confusing. For example, the news department at the journal ''Science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
'' produced an article with the humorous title "Swine Flu Names Evolving Faster Than Swine Flu Itself".
History
Analysis of the genetic divergence of the virus in samples from different cases indicated that the virus jumped to humans in 2008, probably after June, and not later than the end of November,[Alt URL]
/ref> likely around September 2008. The research also indicated the virus had been latent in pigs for several months prior to the outbreak, suggesting a need to increase agricultural surveillance to prevent future outbreaks.[
*] In 2009, U.S. agricultural officials speculated, although emphasizing that there was no way to prove their hypothesis, that "contrary to the popular assumption that the new swine flu pandemic arose on factory farms
Intensive animal farming or industrial livestock production, also known by its opponents as factory farming and macro-farms, is a type of intensive agriculture, specifically an approach to animal husbandry designed to maximize production, while ...
in Mexico, he virus
He or HE may refer to:
Language
* He (pronoun), an English pronoun
* He (kana), the romanization of the Japanese kana へ
* He (letter), the fifth letter of many Semitic alphabets
* He (Cyrillic), a letter of the Cyrillic script called ''He'' ...
most likely emerged in pigs in Asia, but then traveled to North America in a human." However, a subsequent report by researchers at the Mount Sinai School of Medicine
The Icahn School of Medicine at Mount Sinai (ISMMS or Mount Sinai), formerly the Mount Sinai School of Medicine, is a private medical school in New York City. It is the academic teaching arm of the Mount Sinai Health System, which manages eigh ...
in 2016 found that the 2009 H1N1 virus likely originated from pigs in a very small region of central Mexico.
Initially called an "outbreak", widespread H1N1 infection was first recognized in the state of Veracruz
Veracruz (), formally Veracruz de Ignacio de la Llave (), officially the Free and Sovereign State of Veracruz de Ignacio de la Llave ( es, Estado Libre y Soberano de Veracruz de Ignacio de la Llave), is one of the 31 states which, along with Me ...
, Mexico, with evidence that the virus had been present for months before it was officially called an "epidemic". The Mexican government closed most of Mexico City
Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
's public and private facilities in an attempt to contain the spread of the virus; however, it continued to spread globally, and clinics in some areas were overwhelmed by infected people. The new virus was first isolated in late April by American and Canadian laboratories from samples taken from people with flu in Mexico, Southern California, and Texas. Soon the earliest known human case was traced to a case from 9March 2009 in a 5-year-old boy in La Gloria, Mexico, a rural town in Veracruz. In late April, the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) declared its first ever "public health emergency of international concern," or PHEIC
A public health emergency of international concern (PHEIC) is a formal declaration by the World Health Organization (WHO) of "an extraordinary event which is determined to constitute a public health risk to other States through the internatio ...
, and in June, the WHO and the U.S. CDC stopped counting cases and declared the outbreak a pandemic
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...
.
Despite being informally called "swine flu", the H1N1 flu virus cannot be spread by eating pork products; similar to other influenza viruses, it is typically contracted by person to person transmission through respiratory droplets. Symptoms usually last 4–6 days. Antivirals
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...
(oseltamivir
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
or zanamivir
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
) were recommended for those with more severe symptoms or those in an at-risk group.[
The pandemic began to taper off in November 2009,] and by May 2010, the number of cases was in steep decline. On 10 August 2010, the Director-General of the WHO, Margaret Chan
Margaret Chan Fung Fu-chun, (born 21 August 1947) is a Chinese-Canadian physician, who served as the Director-General of the World Health Organization (WHO) delegating the People's Republic of China from 2006–2017. Chan previously served a ...
, announced the end of the H1N1 pandemic and announced that the H1N1 influenza event had moved into the post-pandemic period. According to WHO statistics (as of July 2010), the virus had killed more than 18,000 people since it appeared in April 2009; however, they state that the total mortality (including deaths unconfirmed or unreported) from the H1N1 strain is "unquestionably higher". Critics claimed the WHO had exaggerated the danger, spreading "fear and confusion" rather than "immediate information". The WHO began an investigation to determine whether it had "frightened people unnecessarily". A flu follow-up study done in September 2010, found that "the risk of most serious complications was not elevated in adults or children." In a 5August 2011 ''PLOS ONE'' article, researchers estimated that the 2009 H1N1 global infection rate was 11% to 21%, lower than what was previously expected. However, by 2012, research showed that as many as 579,000 people could have been killed by the disease, as only those fatalities confirmed by laboratory testing were included in the original number, and meant that many without access to health facilities went uncounted. The majority of these deaths occurred in Africa and Southeast Asia. Experts, including the WHO, have agreed that an estimated 284,500 people were killed by the disease, much higher than the initial death toll.
Signs and symptoms
The symptoms of H1N1 flu are similar to those of other influenza
Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms ...
s, and may include fever, cough (typically a "dry cough"), headache, dizziness, sneezing, muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
or joint
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...
pain, sore throat
Sore throat, also known as throat pain, is pain or irritation of the throat. Usually, causes of sore throat include
* viral infections
* group A streptococcal infection (GAS) bacterial infection
* pharyngitis (inflammation of the throat)
* tonsi ...
, chills
Chills is a feeling of coldness occurring during a high fever, but sometimes is also a common symptom which occurs alone in specific people. It occurs during fever due to the release of cytokines and prostaglandins as part of the inflammatory r ...
, fatigue
Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
, and runny nose
Rhinorrhea, rhinorrhoea, or informally runny nose is the free discharge of a thin mucus fluid from the nose; it is a common condition. It is a common symptom of allergies (hay fever) or certain viral infections, such as the common cold or COVID-1 ...
. Diarrhea
Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, vomiting, and neurological
Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...
problems have also been reported in some cases. People at higher risk of serious complications include people over 65, children younger than 5, children with neurodevelopmental conditions, pregnant women (especially during the third trimester), and people of any age with underlying medical conditions, such as asthma, diabetes, obesity, heart disease, or a weakened immune system (e.g., taking immunosuppressive medications or infected with HIV). More than 70% of hospitalizations in the U.S. have been people with such underlying conditions, according to the CDC
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
.
In September 2009, the CDC reported that the H1N1 flu "seems to be taking a heavier toll among chronically ill children than the seasonal flu usually does". Through 8August 2009, the CDC had received 36 reports of pediatric deaths with associated influenza symptoms and laboratory-confirmed pandemic H1N1 from state and local health authorities within the United States, with 22 of these children having neurodevelopmental conditions such as cerebral palsy
Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensa ...
, muscular dystrophy
Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...
, or developmental delay
Global developmental delay is an umbrella term used when children are significantly delayed in their cognitive and physical development. It can be diagnosed when a child is delayed in one or more milestones, categorised into motor skills, speech, c ...
s. "Children with nerve and muscle problems may be at especially high risk for complications because they cannot cough hard enough to clear their airways".[ From 26 April 2009, to 13 February 2010, the CDC had received reports of the deaths of 277 children with laboratory-confirmed 2009 influenza A (H1N1) within the United States.
]
Severe cases
The World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
reports that the clinical picture in severe cases is strikingly different from the disease pattern seen during epidemics of seasonal influenza. While people with certain underlying medical conditions are known to be at increased risk, many severe cases occur in previously healthy people. In severe cases, patients generally begin to deteriorate around three to five days after symptom onset. Deterioration is rapid, with many patients progressing to respiratory failure within 24 hours, requiring immediate admission to an intensive care unit
220px, Intensive care unit
An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
. Upon admission, most patients need immediate respiratory support with mechanical ventilation
Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air ...
.
Complications
Most complications have occurred among previously unhealthy individuals, with obesity
Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...
and respiratory disease
Respiratory diseases, or lung diseases, are pathology, pathological conditions affecting the organs and tissues that make gas exchange difficult in Breathing, air-breathing animals. They include conditions of the respiratory tract including the t ...
as the strongest risk factors. Pulmonary
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...
complications are common. Primary influenza pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
occurs most commonly in adults and may progress rapidly to acute lung injury requiring mechanical ventilation
Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air ...
. Secondary bacterial infection
Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of ...
is more common in children. ''Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...
'', including methicillin-resistant strains, is an important cause of secondary bacterial pneumonia with a high mortality rate; ''Streptococcus pneumoniae
''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They are ...
'' is the second most important cause of secondary bacterial pneumonia for children and primary for adults. Neuromuscular
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber.
It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction.
Muscles require innervation t ...
and cardiac
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
complications are unusual but may occur.
A United Kingdom investigation of risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza looked at 631 patients from 55 hospitals admitted with confirmed infection from May through September 2009. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, cou ...
, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
(COPD) were associated with a severe outcome, as were radiologically confirmed pneumonia and a raised C-reactive protein
C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin-6 ...
(CRP) level (≥. 59% of all in-hospital deaths occurred in previously healthy people.
Fulminant
Fulminant () is a medical descriptor for any event or process that occurs suddenly and escalates quickly, and is intense and severe to the point of lethality, i.e., it has an explosive character. The word comes from Latin ''fulmināre'', to strik ...
(sudden-onset) myocarditis
Myocarditis, also known as inflammatory cardiomyopathy, is an acquired cardiomyopathy due to inflammation of the heart muscle. Symptoms can include shortness of breath, chest pain, decreased ability to exercise, and an irregular heartbeat. The ...
has been linked to infection with H1N1, with at least four cases of myocarditis confirmed in patients also infected with A/H1N1. Three out of the four cases of H1N1-associated myocarditis were classified as fulminant, and one of the patients died.
Also, there appears to be a link between severe A/H1N1 influenza infection and pulmonary embolism
Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...
. In one report, five out of 14 patients admitted to the intensive care unit with severe A/H1N1 infection were found to have pulmonary emboli.
An article published in ''JAMA
''The Journal of the American Medical Association'' (''JAMA'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of biom ...
'' in September 2010 challenged previous reports and stated that children infected in the 2009 flu pandemic were no more likely to be hospitalised with complications or get pneumonia than those who catch seasonal strains. Researchers found that about 1.5% of children with the H1N1 swine flu strain were hospitalised within 30 days, compared with 3.7% of those sick with a seasonal strain of H1N1 and 3.1% with an H3N2 virus.
Diagnosis
Confirmed diagnosis of pandemic H1N1 flu requires testing of a nasopharyngeal
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
, nasal, or oropharyngeal
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
tissue swab from the patient. Real-time
Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...
RT-PCR
Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase cha ...
is the recommended test as others are unable to differentiate between pandemic H1N1 and regular seasonal flu
Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemisphere. It takes approximately two days to show symptoms. Influen ...
. However, most people with flu symptoms do not need a test for pandemic H1N1 flu specifically, because the test results usually do not affect the recommended course of treatment. The U.S. CDC recommend testing only for people who are hospitalized with suspected flu, pregnant women, and people with weakened immune systems. For the mere diagnosis of influenza and not pandemic H1N1 flu specifically, more widely available tests include rapid influenza diagnostic test A rapid influenza diagnostic test (RIDT) tells whether a person has a current influenza infection by detecting the influenza viral nucleoprotein antigen
In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particul ...
s (RIDT), which yield results in about 30 minutes, and direct
Direct may refer to:
Mathematics
* Directed set, in order theory
* Direct limit of (pre), sheaves
* Direct sum of modules, a construction in abstract algebra which combines several vector spaces
Computing
* Direct access (disambiguation), a ...
and indirect immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specif ...
assays ( DFA and IFA), which take 2–4 hours. Due to the high rate of RIDT false negative
A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test result ...
s, the CDC advises that patients with illnesses compatible with novel influenza A (H1N1) virus infection but with negative RIDT results should be treated empirically based on the level of clinical suspicion, underlying medical conditions, severity of illness, and risk for complications, and if a more definitive determination of infection with influenza virus is required, testing with rRT-PCR or virus isolation should be performed. The use of RIDTs has been questioned by researcher Paul Schreckenberger of the Loyola University Health System, who suggests that rapid tests may actually pose a dangerous public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
risk. Nikki Shindo of the WHO has expressed regret at reports of treatment being delayed by waiting for H1N1 test results and suggests, " ctors should not wait for the laboratory confirmation but make diagnosis based on clinical and epidemiological backgrounds and start treatment early."
On 22 June 2010, the CDC announced a new test called the "CDC Influenza 2009 A (H1N1)pdm Real-Time RT-PCR Panel (IVD)". It uses a molecular biology technique to detect influenza A viruses and specifically the 2009 H1N1 virus. The new test will replace the previous real-time RT-PCR diagnostic test used during the 2009 H1N1 pandemic, which received an emergency use authorization from the U.S. Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...
in April 2009. Tests results are available in four hours and are 96% accurate.
Cause
The virus was found to be a novel strain of influenza for which existing vaccines
A vaccine is a biological preparation that provides active acquired immunity
The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and pro ...
against seasonal flu provided little protection. A study at the U.S. Centers for Disease Control and Prevention published in May 2009 found that children had no preexisting immunity to the new strain but that adults, particularly those older than 60, had some degree of immunity
Immunity may refer to:
Medicine
* Immunity (medical), resistance of an organism to infection or disease
* ''Immunity'' (journal), a scientific journal published by Cell Press
Biology
* Immune system
Engineering
* Radiofrequence immunity desc ...
. Children showed no cross-reactive antibody
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
reaction to the new strain, adults aged 18 to 60 had 6–9%, and older adults 33%. While it has been thought that these findings suggest the partial immunity in older adults may be due to previous exposure to similar seasonal influenza viruses, a November 2009 study of a rural unvaccinated population in China found only a 0.3% cross-reactive antibody reaction to the H1N1 strain, suggesting that previous vaccinations for seasonal flu and not exposure may have resulted in the immunity found in the older U.S. population.
Analyses of the genetic sequences of the first isolates, promptly shared on the GISAID
GISAID (Global Initiative on Sharing Avian Influenza Data) is a global science initiative and primary source established in 2008 that provides open access to genomic data of influenza viruses and the coronavirus responsible for the COVID-19 pan ...
database according to Nature and WHO, soon determined that the strain contains genes from five different flu viruses: North American swine influenza, North American avian influenza, human influenza, and two swine influenza viruses typically found in Asia and Europe. Further analysis has shown that several protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s of the virus are most similar to strains that cause mild symptoms in humans, leading virologist
Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, thei ...
Wendy Barclay to suggest on 1May 2009, that the initial indications are that the virus was unlikely to cause severe symptoms for most people.
The virus was less lethal than previous pandemic strains and killed about 0.01–0.03% of those infected; the 1918 influenza was about one hundred times more lethal and had a case fatality rate of 2–3%. By 14 November 2009, the virus had infected one in six Americans with 200,000 hospitalisations and 10,000 deaths—as many hospitalizations and fewer deaths than in an average flu season overall, but with much higher risk for those under 50. With deaths of 1,100 children and 7,500 adults 18 to 64, these figures were deemed "much higher than in a usual flu season" during the pandemic.
In June 2010, scientists from Hong Kong reported discovery of a new swine flu virus: a hybrid of the pandemic H1N1 virus and viruses previously found in pigs. It was the first report of a reassortment of the pandemic virus, which in humans had been slow to evolve. Nancy Cox Nancy Cox may refer to:
* Nancy Cox (virologist) (born 1949), American virologist
* Nancy Cox (TV news anchor)
Nancy Jane Cox is an American television journalist and news anchor for WLEX-TV in Lexington, Kentucky, Lexington, Kentucky. She was als ...
, head of the influenza division at the U.S. Centers for Disease Control and Prevention, has said, "This particular paper is extremely interesting because it demonstrates for the first time what we had worried about at the very onset of the pandemic, and that is that this particular virus, when introduced into pigs, could reassort with the resident viruses in pigs and we would have new gene constellations. And bingo, here we are." Pigs have been termed the mixing vessel of flu because they can be infected both by avian flu viruses, which rarely directly infect people, and by human viruses. When pigs become simultaneously infected with more than one virus, the viruses can swap genes, producing new variants which can pass to humans and sometimes spread amongst them. "Unlike the situation with birds and humans, we have a situation with pigs and humans where there's a two-way street of exchange of viruses. With pigs it's very much a two-way street."
Transmission
Spread of the H1N1 virus is thought to occur in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing by people with influenza. Sometimes people may become infected by touching something—such as a surface or object—with flu viruses on it and then touching their face.
The basic reproduction number
In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted R_0 (pronounced ''R nought'' or ''R zero''), of an infection is the expected number of ...
(the average number of other individuals whom each infected individual will infect, in a population which has no immunity to the disease) for the 2009 novel H1N1 is estimated to be 1.75. A December 2009 study found that the transmissibility of the H1N1 influenza virus in households is lower than that seen in past pandemics. Most transmissions occur soon before or after the onset of symptoms.
The H1N1 virus has been transmitted to animals, including swine, turkeys
The turkey is a large bird in the genus ''Meleagris'', native to North America. There are two extant turkey species: the wild turkey (''Meleagris gallopavo'') of eastern and central North America and the ocellated turkey (''Meleagris ocellat ...
, ferret
The ferret (''Mustela furo'') is a small, Domestication, domesticated species belonging to the family Mustelidae. The ferret is most likely a domesticated form of the wild European polecat (''Mustela putorius''), evidenced by their Hybrid (biol ...
s, household cats, at least one dog, and a cheetah
The cheetah (''Acinonyx jubatus'') is a large cat native to Africa and central Iran. It is the fastest land animal, estimated to be capable of running at with the fastest reliably recorded speeds being , and as such has evolved specialized ...
.
Prevention
Because the H1N1 vaccine was initially in short supply in the U.S., the CDC recommended that initial doses should go to priority groups such as pregnant women, people who live with or care for babies under six months old, children six months to four years old and health-care workers. In the UK, the NHS recommended vaccine priority go to people over six months old who were clinically at risk for seasonal flu, pregnant women and households of people with compromised immunity.
Although it was initially thought that two injections would be required, clinical trials showed that the new vaccine protected adults "with only one dose instead of two;" thus the limited vaccine supplies would go twice as far as had been predicted. Health officials worldwide were also concerned because the virus was new and could easily mutate and become more virulent, even though most flu symptoms were mild and lasted only a few days without treatment. Officials also urged communities, businesses, and individuals to make contingency plans for possible school closures, multiple employee absences for illness, surges of patients in hospitals, and other effects of potentially widespread outbreaks. Disaster response organizations such as Direct Relief helped by providing protective items to clinical workers to help them stay healthy throughout flu season.
In February 2010, the CDC's Advisory Committee on Immunization Practices voted for "universal" flu vaccination in the U.S. to include all people over six months of age. The 2010–2011 vaccine will protect against the 2009 H1N1 pandemic virus and two other flu viruses.
Public health response
On 27 April 2009, the European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
health commissioner advised Europeans to postpone nonessential travel to the United States or Mexico. This followed the discovery of the first confirmed case in Spain. On 6May 2009, the Public Health Agency of Canada
The Public Health Agency of Canada (PHAC; french: Agence de la santé publique du Canada, ASPC) is an agency of the Government of Canada that is responsible for public health, emergency preparedness and response, and infectious and chronic diseas ...
announced that their National Microbiology Laboratory
The National Microbiology Laboratory (NML) is part of the Public Health Agency of Canada (PHAC), the agency of the Government of Canada that is responsible for public health, health emergency preparedness and response, and infectious and chronic d ...
(NML) had mapped the genetic code of the swine flu virus, the first time that had been done. In the U.K., the National Health Service
The National Health Service (NHS) is the umbrella term for the publicly funded healthcare systems of the United Kingdom (UK). Since 1948, they have been funded out of general taxation. There are three systems which are referred to using the " ...
launched a website, the National Pandemic Flu Service, allowing patients to self-assess and get an authorisation number for antiviral medication. The system was expected to reduce the burden on general practitioners.
U.S. officials observed that six years of concern about H5N1
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other animal species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of typ ...
avian flu
Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. did much to prepare for the current H1N1 outbreak, noting that after H5N1 emerged in Asia, ultimately killing about 60% of the few hundred people infected over the years, many countries took steps to try to prevent any similar crisis from spreading further. The CDC and other U.S. governmental agencies used the summer lull to take stock of the United States response to H1N1 flu and attempt to patch any gaps in the public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
safety net before flu season started in early autumn. Preparations included planning a second influenza vaccination program in addition to the one for seasonal flu, and improving coordination between federal, state, and local governments and private health providers. On 24 October 2009, U.S. President Obama
Barack Hussein Obama II ( ; born August 4, 1961) is an American politician who served as the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, Obama was the first African-American president of the U ...
declared swine flu a national emergency, giving Secretary of Health and Human Services
The United States secretary of health and human services is the head of the United States Department of Health and Human Services, and serves as the principal advisor to the president of the United States on all health matters. The secretary is ...
Kathleen Sebelius
Kathleen Sebelius (; née Gilligan, born May 15, 1948) is an American businesswoman and politician who served as the 21st United States secretary of Health and Human Services from 2009 until 2014. As Secretary of Health and Human Services, Sebeli ...
authority to grant waivers to requesting hospitals from usual federal requirements.
Vaccines
By 19 November 2009, doses of vaccine had been administered in over 16 countries. A 2009 review by the U.S. National Institutes of Health (NIH) concluded that the 2009 H1N1 vaccine has a safety profile similar to that of the seasonal vaccine.
In 2011, a study from the US Flu Vaccine Effectiveness Network estimated the overall effectiveness of all pandemic H1N1 vaccines at 56%. A CDC study released 28 January 2013, estimated that the Pandemic H1N1 vaccine saved roughly 300 lives and prevented about a million illnesses in the US. The study concluded that had the vaccination program started two weeks earlier, close to 60% more cases could have been prevented. The study was based on an effectiveness in preventing cases, hospitalizations, and deaths of 62% for all subgroups except people over 65, for whom the effectiveness was estimated at 43%. The effectiveness was based on European and Asian studies and expert opinion. The delay in vaccine administration demonstrated the shortcomings of the world's capacity for vaccine-production, as well as problems with international distribution. Some manufacturers and wealthy countries had concerns regarding liability and regulations, as well as the logistics of transporting, storing, and administering vaccines to be donated to poorer countries.
Accusations of conflict of interest
In January 2010, Wolfgang Wodarg, a German deputy who trained as a physician and chaired the health committee at the Council of Europe
The Council of Europe (CoE; french: Conseil de l'Europe, ) is an international organisation founded in the wake of World War II to uphold European Convention on Human Rights, human rights, democracy and the Law in Europe, rule of law in Europe. ...
, claimed that major firms had organized a "campaign of panic" to put pressure on the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) to declare a "false pandemic" to sell vaccines. Wodarg said the WHO's "false pandemic" flu campaign is "one of the greatest medicine scandals of the century". He said that the "false pandemic" campaign began in May 2009 in Mexico City
Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
, when a hundred or so "normal" reported influenza cases were declared to be the beginning of a threatening new pandemic, although he said there was little scientific evidence for it. Nevertheless, he argued that the WHO, "in cooperation with some big pharmaceutical companies and their scientists, re-defined pandemics," removing the statement that "an enormous amount of people have contracted the illness or died" from its existing definition and replacing it by stating simply that there has to be a virus, spreading beyond borders and to which people have no immunity.
The WHO responded by stating that they take their duty to provide independent advice seriously and guarded against interference from outside interests. Announcing a review of the WHO's actions, spokeswoman Fadela Chaib stated: "Criticism is part of an outbreak cycle. We expect and indeed welcome criticism and the chance to discuss it". The WHO also stated on their website that "The world is going through a real pandemic. The description of it as a fake is wrong and irresponsible". In March 2010, the Council of Europe launched an enquiry into "the influence of the pharmaceutical companies on the global swine flu campaign", and a preliminary report was in preparation.
On 12 April 2010, Keiji Fukuda, the WHO's top influenza expert, stated that the system leading to the declaration of a pandemic led to confusion about H1N1 circulating around the world and he expressed concern that there was a failure to communicate in regard to uncertainties about the new virus, which turned out to be not as deadly as feared. WHO Director-General Margaret Chan appointed 29 flu experts from outside the organization to conduct a review of WHO's handling of the H1N1 flu pandemic. She told them, "We want a frank, critical, transparent, credible and independent review of our performance."
In June 2010, Fiona Godlee
Fiona Godlee (born August 4, 1961) was editor in chief of ''The British Medical Journal'' from March 2005 until 31 December 2021; she was the first female editor appointed in the journal's history. She was also editorial director of the other jou ...
, editor-in-chief of the ''BMJ
''The BMJ'' is a weekly peer-reviewed medical trade journal, published by the trade union the British Medical Association (BMA). ''The BMJ'' has editorial freedom from the BMA. It is one of the world's oldest general medical journals. Origina ...
'', published an editorial which criticised the WHO, saying that an investigation had disclosed that some of the experts advising WHO on the pandemic had financial ties with drug companies which were producing antivirals and vaccines. Margaret Chan, Director-General of the WHO, replied stating, "Without question, the ''BMJ'' feature and editorial will leave many readers with the impression that WHO's decision to declare a pandemic was at least partially influenced by a desire to boost the profits of the pharmaceutical industry. The bottom line, however, is that decisions to raise the level of pandemic alert were based on clearly defined virological and epidemiological criteria. It is hard to bend these criteria, no matter what the motive".[
]
Infection control
Travel precautions
On 7 May 2009, the WHO stated that containment was not feasible and that countries should focus on mitigating the effect of the virus. They did not recommend closing borders or restricting travel. On 26 April 2009, the Chinese government
The Government of the People's Republic of China () is an authoritarian political system in the People's Republic of China under the exclusive political leadership of the Chinese Communist Party (CCP). It consists of legislative, executive, mili ...
announced that visitors returning from flu-affected areas who experienced flu-like symptoms within two weeks would be quarantined.
U.S. airlines had made no major changes as of the beginning of June 2009, but continued standing practices which include looking for passengers with symptoms of flu, measles
Measles is a highly contagious infectious disease caused by measles virus. Symptoms usually develop 10–12 days after exposure to an infected person and last 7–10 days. Initial symptoms typically include fever, often greater than , cough, ...
or other infections, and relying on in-flight air filter
A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...
s to ensure that aircraft were sanitised. Masks were not generally provided by airlines and the CDC did not recommend that airline crews wear them. Some non-U.S. airlines, mostly Asian, including Singapore Airlines
Singapore Airlines (abbreviation: SIA) is the flag carrier airline of the Republic of Singapore with its Airline hub, hub located at Singapore Changi Airport. The airline is notable for highlighting the Singapore Girl as its central figure in ...
, China Eastern Airlines
China Eastern Airlines Corporation Limited (), also known as China Eastern, is an airline headquartered in the China Eastern Airlines Building, on the grounds of Shanghai Hongqiao International Airport in Changning District, Shanghai. It is ...
, China Southern Airlines
China Southern Airlines Company Limited is an airline headquartered in Baiyun District, Guangzhou, Baiyun District, Guangzhou, Guangdong Province and is the largest airline in China. Established on 1 July 1988 following the restructuring of ...
, Cathay Pacific
Cathay Pacific Airways Limited (CPA), more widely known as Cathay Pacific (), is the flag carrier of Hong Kong, with its head office and main hub located at Hong Kong International Airport. The airline's operations and subsidiaries have sc ...
and Aeromexico, took measures such as stepping up cabin cleaning, installing state-of-the-art air filters and allowing in-flight staff to wear face masks.
According to studies conducted in Australia and Japan, screening individuals for influenza symptoms at airports during the 2009 H1N1 outbreak was not an effective method of infection control.
Schools
U.S. government officials were especially concerned about schools because the H1N1 flu virus appeared to disproportionately affect young and school-age people, between six months and 24 years of age.
The H1N1 outbreak led to numerous precautionary school closures in some areas. Rather than closing schools, the CDC recommended that students and school workers with flu symptoms should stay home for either seven days total, or until 24 hours after symptoms subsided, whichever was longer. The CDC also recommended that colleges should consider suspending fall 2009 classes if the virus began to cause severe illness in a significantly larger share of students than the previous spring. They also urged schools to suspend rules, such as penalties for late papers or missed classes or requirements for a doctor's note, to enforce "self-isolation" and prevent students from venturing out while ill; schools were advised to set aside a room for people developing flu-like symptoms while they waited to go home and to have ill students or staff and those caring for them use face masks.
In California, school districts and universities were on alert and worked with health officials to launch education campaigns. Many planned to stockpile medical supplies and discuss worst-case scenarios, including plans to provide lessons and meals for low-income children in case elementary and secondary schools closed. University of California
The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, ...
campuses stockpiled supplies, from paper masks and hand sanitizer to food and water.[
] To help prepare for contingencies, University of Maryland School of Medicine
The University of Maryland School of Medicine (abbreviated UMSOM), located in Baltimore City, Maryland, U.S., is the medical school of the University of Maryland, Baltimore and is affiliated with the University of Maryland Medical Center and Me ...
professor of pediatrics
Pediatrics ( also spelled ''paediatrics'' or ''pædiatrics'') is the branch of medicine that involves the medical care of infants, children, adolescents, and young adults. In the United Kingdom, paediatrics covers many of their youth until th ...
James C. King Jr. suggested that every county should create an "influenza action team" to be run by the local health department
A health department or health ministry is a part of government which focuses on issues related to the general health of the citizenry. Subnational entities, such as states, counties and cities, often also operate a health department of their ow ...
, parents, and school administrators. By 28 October 2009, about 600 schools in the United States had been temporarily closed, affecting over 126,000 students in 19 states.
Workplace
Fearing a worst-case scenario, the U.S. Department of Health and Human Services
The United States Department of Health and Human Services (HHS) is a cabinet-level executive branch department of the U.S. federal government created to protect the health of all Americans and providing essential human services. Its motto is " ...
(HHS), the Centers for Disease Control and Prevention and the Department of Homeland Security
The United States Department of Homeland Security (DHS) is the U.S. federal executive department responsible for public security, roughly comparable to the interior or home ministries of other countries. Its stated missions involve anti-terr ...
(DHS) developed updated guidance and a video for employers to use as they developed plans to respond to the H1N1 outbreak. The guidance suggested that employers consider and communicate their objectives, such as reducing transmission among staff, protecting people who are at increased risk of influenza-related complications from becoming infected, maintaining business operations, and minimising adverse effects on other entities in their supply chain
In commerce, a supply chain is a network of facilities that procure raw materials, transform them into intermediate goods and then final products to customers through a distribution system. It refers to the network of organizations, people, acti ...
s.
The CDC estimated that as much as 40% of the workforce might be unable to work at the peak of the pandemic due to the need for many healthy adults to stay home and care for an ill family member,[
] and advised that individuals should have steps in place should a workplace close down or a situation arise that requires remote work
Remote work, also called work from home (WFH), work from anywhere, telework, remote job, mobile work, and distance work is an employment arrangement in which employees do not commute to a central place of work, such as an office building, ware ...
. The CDC further advised that persons in the workplace should stay home sick for seven days after getting the flu, or 24 hours after symptoms end, whichever is longer.[
In the UK, the ]Health and Safety Executive
The Health and Safety Executive (HSE) is a UK government agency responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks in Great Britain. It is a non-depar ...
(HSE) also issued general guidance for employers.
Face masks
The U.S. CDC did not recommend the use of face masks or respirator
A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of respir ...
s in non-health care settings, such as schools, workplaces, or public places, with a few exceptions: people who were ill with the virus when around other people, and people who were at risk for severe illness while caring for someone with the flu.[
] There was some disagreement about the value of wearing face masks, as some experts feared that masks may have given people a false sense of security and should not have replaced other standard precautions.[
]
Yukihiro Nishiyama, professor of virology at Nagoya University
, abbreviated to or NU, is a Japanese national research university located in Chikusa-ku, Nagoya. It was the seventh Imperial University in Japan, one of the first five Designated National University and selected as a Top Type university of T ...
's School of Medicine, commented that the masks are "better than nothing, but it's hard to completely block out an airborne virus since it can easily slip through the gaps".
According to mask manufacturer 3M, masks will filter out particles
In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.
They vary greatly in size or quantity, from s ...
in industrial settings, but "there are no established exposure limits for biological agent
A biological agent (also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon) is a bacterium, virus, protozoan, parasite, fungus, or toxin that can be used purposefully as a weapon in bioterroris ...
s such as swine flu virus". However, despite the lack of evidence of effectiveness, the use of such masks is common in Asia.
They are particularly popular in Japan, where cleanliness and hygiene are highly valued and where etiquette obligates those who are sick to wear masks to avoid spreading disease.
Quarantine
During the height of the fear of a pandemic, some countries initiated or threatened to initiate quarantine
A quarantine is a restriction on the movement of people, animals and goods which is intended to prevent the spread of disease or pests. It is often used in connection to disease and illness, preventing the movement of those who may have been ...
s of foreign visitors suspected of having or being in contact with others who may have been infected. In May 2009, the Chinese government confined 21 U.S. students and three teachers to their hotel rooms. As a result, the US State Department
The United States Department of State (DOS), or State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs of other nati ...
issued a travel alert about China's anti-flu measures and warned travellers against travelling to China if ill. In Hong Kong, an entire hotel was quarantined with 240 guests; Australia ordered a cruise ship with 2,000 passengers to stay at sea because of a swine flu threat. Egyptian Muslims who went on the annual pilgrimage
A pilgrimage is a journey, often into an unknown or foreign place, where a person goes in search of new or expanded meaning about their self, others, nature, or a higher good, through the experience. It can lead to a personal transformation, aft ...
to Mecca
Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the Holiest sites in Islam, holiest city in Islam. It is inland from Jeddah on the Red ...
risked being quarantined upon their return. Russia and Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
said they would quarantine visitors with fevers who come from areas where the flu was present. Japan quarantined 47 airline passengers in a hotel for a week in mid-May, then in mid-June India suggested pre-screening "outbound" passengers from countries thought to have a high rate of infection.
Pigs and food safety
The pandemic virus is a type of swine influenza, derived originally from a strain which lived in pigs, and this origin gave rise to the common name of "swine flu". This term is widely used by mass media, though the Paris-based World Organisation for Animal Health
The World Organisation for Animal Health (WOAH), formerly the (OIE), is an intergovernmental organization coordinating, supporting and promoting animal disease control.
Mission and status
The main objective of the WOAH is to control epizoo ...
as well as industry groups such as the U.S. National Pork Board The National Pork Board is a program sponsored by the United States Department of Agriculture Agricultural Marketing Service whose purpose is to provide consumer information, perform industry-related research, and promote pork as a food product. The ...
, the American Meat Institute
The American Meat Institute (AMI) was the oldest and largest trade association representing the U.S. meat and poultry industry. In 2015, it was merged into the North American Meat Institute (NAMI).
Overview
Founded in 1906 in Chicago as the Amer ...
, and the Canadian Pork Council objected to widespread media use of the name "swine flu" and suggested it should be called "North American flu" instead, while the World Health Organization switched its designation from "swine influenza" to "influenza A (H1N1)" in late April 2009. The virus has been found in U.S. hogs, and Canadian as well as in hogs in Northern Ireland, Argentina, and Norway. Leading health agencies and the United States Secretary of Agriculture
The United States secretary of agriculture is the head of the United States Department of Agriculture. The position carries similar responsibilities to those of agriculture ministers in other governments.
The department includes several organi ...
have stressed that eating properly cooked pork or other food products derived from pigs will not cause flu. Nevertheless, on 27 April Azerbaijan
Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan, , also sometimes officially called the Azerbaijan Republic is a transcontinental country located at the boundary of Eastern Europe and Western Asia. It is a part of th ...
imposed a ban on the importation of animal husbandry
Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, starti ...
products from the entire Americas
The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World.
Along with th ...
. The Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
n government also halted the importation of pigs and initiated the examination of pigs in Indonesia. The Egyptian government ordered the slaughter of all pigs in Egypt on 29 April.
Treatment
A number of methods have been recommended to help ease symptoms, including adequate liquid intake and rest. Over-the-counter
Over-the-counter (OTC) drugs are medicines sold directly to a consumer without a requirement for a prescription from a healthcare professional, as opposed to prescription drugs, which may be supplied only to consumers possessing a valid prescr ...
pain medications such as paracetamol
Paracetamol, also known as acetaminophen, is a medication used to treat fever and mild to moderate pain. Common brand names include Tylenol and Panadol.
At a standard dose, paracetamol only slightly decreases body temperature; it is inferior ...
and ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is used for treating pain, fever, and inflammation. This includes painful menstrual periods, migraines, and rheumatoid arthritis. It may also be used to close a patent ductus arte ...
do not kill the virus; however, they may be useful to reduce symptoms. Aspirin
Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and/or inflammation, and as an antithrombotic. Specific inflammatory conditions which aspirin is used to treat inc ...
and other salicylate products should not be used by people under 16 with any flu-type symptoms because of the risk of developing Reye's Syndrome
Reye syndrome is a rapidly worsening encephalopathy, brain disease. Symptoms of Reye syndrome may include vomiting, personality changes, confusion, seizures, and loss of consciousness. While hepatotoxicity, liver toxicity typically occurs in the ...
.
If the fever is mild and there are no other complications, fever medication is not recommended. Most people recover without medical attention, although ones with pre-existing or underlying medical conditions are more prone to complications and may benefit from further treatments.
People in at-risk groups should be treated with antivirals
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...
(oseltamivir or zanamivir) as soon as possible when they first experience flu symptoms. The at-risk groups include pregnant and post partum
The postpartum (or postnatal) period begins after childbirth and is typically considered to end within 6 weeks as the mother's body, including hormone levels and uterus size, returns to a non-pregnant state. The terms puerperium, puerperal perio ...
women, children under two years old, and people with underlying conditions such as respiratory problems.[ People who are not in an at-risk group who have persistent or rapidly worsening symptoms should also be treated with antivirals. People who have developed ]pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
should be given both antivirals and antibiotics, as in many severe cases of H1N1-caused illness, bacterial infection develops. Antivirals are most useful if given within 48 hours of the start of symptoms and may improve outcomes in hospitalised patients. In those beyond 48 hours who are moderately or severely ill, antivirals may still be beneficial. If oseltamivir
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
(Tamiflu) is unavailable or cannot be used, zanamivir
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
(Relenza) is recommended as a substitute. Peramivir
Peramivir (trade name Rapivab) is an antiviral drug developed by BioCryst Pharmaceuticals for the treatment of influenza. Peramivir is a neuraminidase inhibitor, acting as a transition-state analogue inhibitor of influenza neuraminidase and th ...
is an experimental antiviral drug
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do n ...
approved for hospitalised patients in cases where the other available methods of treatment are ineffective or unavailable.
To help avoid shortages of these drugs, the U.S. CDC recommended oseltamivir treatment primarily for people hospitalised with pandemic flu; people at risk of serious flu complications due to underlying medical conditions; and patients at risk of serious flu complications. The CDC warned that the indiscriminate use of antiviral medications to prevent and treat influenza could ease the way for drug-resistant strains to emerge, which would make the fight against the pandemic that much harder. In addition, a British report found that people often failed to complete a full course of the drug or took the medication when not needed.
Side effects
Both medications mentioned above for treatment, oseltamivir and zanamivir, have known side effects, including lightheadedness, chills, nausea, vomiting, loss of appetite, and trouble breathing. Children were reported to be at increased risk of self-injury and confusion after taking oseltamivir.[ The WHO warned against buying antiviral medications from online sources and estimated that half the drugs sold by online pharmacies without a physical address were counterfeit.]
Resistance
In December 2012, the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) reported 314 samples of the 2009 pandemic H1N1 flu tested worldwide have shown resistance to oseltamivir
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
(Tamiflu
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
).[
] It is not totally unexpected as 99.6% of the seasonal H1N1 flu strains tested have developed resistance to oseltamivir. No circulating flu has yet shown any resistance to zanamivir
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
(Relenza
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ...
), the other available anti-viral.
Antivirals effectiveness questioned in healthy adults
On 8 December 2009, the Cochrane Collaboration
Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health profess ...
, which reviews medical evidence, announced in a review published in ''BMJ
''The BMJ'' is a weekly peer-reviewed medical trade journal, published by the trade union the British Medical Association (BMA). ''The BMJ'' has editorial freedom from the BMA. It is one of the world's oldest general medical journals. Origina ...
'' that it had reversed its previous findings that the antiviral drugs oseltamivir
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
(Tamiflu) and zanamivir
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
(Relenza) can ward off pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
and other serious conditions linked to influenza. They reported that an analysis of 20 studies showed oseltamivir offered mild benefits for healthy adults if taken within 24 hours of onset of symptoms, but found no clear evidence it prevented lower respiratory tract infections or other complications of influenza. Of note, their published finding related only to use in healthy adults with influenza but not in patients judged to be at high risk of complications (pregnant women, children under five and those with underlying medical conditions), and uncertainty over its role in reducing complications in healthy adults still left it as a useful drug for reducing the duration of symptoms. In general, the Cochrane Collaboration concluded "Paucity of good data".[
]
Epidemiology
While it is not known precisely where or when the virus originated, analyses in scientific journals have suggested that the H1N1 strain responsible for the 2009 outbreak first evolved in September 2008 and circulated amongst humans for several months, before being formally recognised and identified as a novel strain of influenza.
Mexico
The virus was first reported in two U.S. children in March 2009, but health officials have reported that it apparently infected people as early as January 2009 in Mexico. The outbreak was first identified in Mexico City
Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
on 18 March 2009; immediately after the outbreak was officially announced, Mexico notified the U.S. and World Health Organization, and within days of the outbreak Mexico City was "effectively shut down". Some countries cancelled flights to Mexico while others halted trade. Calls to close the border to contain the spread were rejected. Mexico already had hundreds of non-lethal cases before the outbreak was officially discovered, and was therefore in the midst of a "silent epidemic". As a result, Mexico was reporting only the most serious cases which showed more severe signs different from those of normal flu, possibly leading to a skewed initial estimate of the case fatality rate.
United States
The new strain was first identified by the CDC in two children, neither of whom had been in contact with pigs. The first case, from San Diego County, California
San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the fi ...
, was confirmed from clinical specimens (nasopharyngeal
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
swab) examined by the CDC on 14 April 2009. A second case, from nearby Imperial County, California
Imperial County is a County (United States), county on the southeast border of the U.S. state of California. As of the 2020 United States Census, 2020 census, the population was 179,702, making it the least populous county in Southern Californi ...
, was confirmed on 17 April. The patient in the first confirmed case had flu symptoms including fever and cough upon clinical examination on 30 March and the second on 28 March.
The first confirmed H1N1/09 pandemic flu death, which occurred at Texas Children's Hospital Texas Children's Hospital is a nationally ranked, freestanding 973-bed, acute care women's and children's hospital located in Houston, Texas. It is the primary pediatric teaching hospital affiliated with Baylor College of Medicine and is located wit ...
in Houston, Texas, was of a toddler from Mexico City who was visiting family in Brownsville, Texas
Brownsville () is a city in Cameron County in the U.S. state of Texas. It is on the western Gulf Coast in South Texas, adjacent to the border with Matamoros, Mexico. The city covers , and has a population of 186,738 as of the 2020 census. It ...
, before being air-lifted to Houston for treatment. The Infectious Diseases Society of America estimated that the total number of deaths in the U.S. was 12,469.
Data reporting and accuracy
Influenza surveillance information "answers the questions of where, when, and what influenza viruses are circulating. Sharing of such information is especially crucial during an emergent pandemic as in April 2009, when the genetic sequences of the initial viruses were rapidly and openly shared via the GISAID Initiative within days of identification, playing a key role in facilitating an early response to the evolving pandemic. Surveillance is used to determine if influenza activity is increasing or decreasing, but cannot be used to ascertain how many people have become ill with influenza." For example, as of late June, influenza surveillance information showed the U.S. had nearly 28,000 laboratory-confirmed cases including 3,065 hospitalizations and 127 deaths. But mathematical modelling showed an estimated Americans had the 2009 pandemic flu at the time, according to Lyn Finelli, a flu surveillance official with the CDC. Estimating deaths from influenza is also a complicated process. In 2005, influenza only appeared on the death certificates of 1,812 people in the US. The average annual US death toll from flu is, however, estimated to be 36,000. The CDC explains: " fluenza is infrequently listed on death certificates of people who die from flu-related complications" and hence, "Only counting deaths where influenza was included on a death certificate would be a gross underestimation of influenza's true impact."
Influenza surveillance information on the 2009 H1N1 flu pandemic is available, but almost no studies attempted to estimate the total number of deaths attributable to H1N1 flu. Two studies were carried out by the CDC; the later of them estimated that between 7,070 and 13,930 deaths were attributable to H1N1 flu from April to 14 November 2009. During the same period, 1,642 deaths were officially confirmed as caused by H1N1 flu. The WHO stated in 2010 that total mortality (including unconfirmed or unreported deaths) from H1N1 flu was "unquestionably higher" than their own confirmed death statistics.
The initial outbreak received a week of near-constant media attention. Epidemiologist
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evidenc ...
s cautioned that the number of cases reported in the early days of an outbreak can be very inaccurate and deceptive, due to several causes, among them selection bias
Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population int ...
, media bias
Media bias is the bias of journalists and news producers within the mass media in the selection of many events and stories that are reported and how they are covered. The term "media bias" implies a pervasive or widespread bias contravening of ...
and incorrect reporting by governments. Inaccuracies could also be caused by authorities in different countries looking at differing population groups. Furthermore, countries with poor health care systems and older laboratory facilities may take longer to identify or report cases. " en in developed countries the umbers of flu deathsare uncertain, because medical authorities don't usually verify who actually died of influenza and who died of a flu-like illness". Joseph S. Bresee, then CDC flu division's epidemiology chief and Michael Osterholm
Michael Thomas Osterholm (born March 10, 1953) is an American epidemiologist, Regents Professor, and Director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
On November 9, 2020, Osterholm was named to ...
, director of the Center for Infectious Disease Research and Policy
The Center for Infectious Disease Research and Policy (CIDRAP) is a center within the University of Minnesota that focuses on addressing public health preparedness and emerging infectious disease response. It was founded in 2001 by Dr. Michael Os ...
pointed out that millions of people have had H1N1 flu, usually in a mild form, so the numbers of laboratory-confirmed cases were actually meaningless, and in July 2009, the WHO stopped keeping count of individual cases and focused more on major outbreaks.
Follow-up
A Wisconsin study published in the ''Journal of the American Medical Association
''The Journal of the American Medical Association'' (''JAMA'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of bio ...
'' in September 2010, reported that findings showed that the 2009 H1N1 flu was no more severe than the seasonal flu. "The risk of most serious complications was not elevated in adults or children", the study's authors wrote. "Children were disproportionately affected by 2009 H1N1 infection, but the perceived severity of symptoms and risk of serious outcomes were not increased." Children infected in the 2009 H1N1 flu pandemic were no more likely to be hospitalized with complications or get pneumonia than those who catch seasonal strains. About 1.5% of children with the H1N1 swine flu strain were hospitalized within 30 days, compared with 3.7% of those sick with a seasonal strain of H1N1 and 3.1% with an H3N2 virus.
CDC illness and death estimates from April 2009 to April 2010, in the US are as follows:
* between 43 million and 89 million cases of 2009 H1N1 occurred between April 2009 and 10 April 2010. The mid-level in this range is about 61 million people infected with 2009 H1N1.
* between about 195,000 and 403,000 H1N1-related hospitalizations occurred between April 2009 and 10 April 2010. The mid-level in this range is about 274,000 2009 H1N1-related hospitalizations.
* between about 8,870 and 18,300 2009 H1N1-related deaths occurred between April 2009 and 10 April 2010. The mid-level in this range is about 12,470 2009 H1N1-related deaths.
It has been stated that about 36,000 die from the seasonal flu in the U.S. each year, and this is frequently understood as an indication that the H1N1 strain was not as severe as seasonal influenza. The 36,000 estimate was presented in a 2003 study by CDC scientists and refers to a period from 1990 to 1991 through 1998–99. During those years, the number of estimated deaths ranged from 17,000 to 52,000, with an average of about 36,000. Throughout that decade, influenza A (H3N2) was the predominant virus during most of the seasons, and H3N2 influenza viruses are typically associated with higher death rates. The ''JAMA'' study also looked at seasonal influenza-associated deaths over a 23-year period, from 1976 to 1977 and 1998–99 with estimates of respiratory and circulatory influenza-associated deaths ranging from about 5,000 to about 52,000, and an average of about 25,000. CDC believes that the range of deaths over the past 31 years (~3,000 to ~49,000) is a more accurate representation of the unpredictability and variability of flu-associated deaths. The annual toll from seasonal influenza in the US between 1979 and 2001 is estimated at 41,400 deaths on average. Therefore, the H1N1 pandemic estimated mortality of 8,870 to 18,300 is just below the mid-range of estimates.
The 2009 pandemic caused US hospitals to make significant preparations in terms of hospital surge capacities, especially within the emergency department and among vulnerable populations. In many cases, hospitals were relatively successful in making sure that those patients most severely affected by the influenza strain were able to be seen, treated, and discharged in an efficient manner. A case-study of the preparation, planning, mitigation, and response efforts during the fall of 2009 is that of the Children's Hospital of Philadelphia (CHOP) which took several steps to increase the emergency department (ED) surge capacity response. CHOP used portions of the main lobby area as an ED waiting room; several of the region's hospital-based outpatient facilities were in use during evening and weekend hours for non-emergency cases; the ED's 24-hour short-stay unit was utilized to care for ED patients in a longer-term capacity; non-board certified physicians (in pediatric emergency medicine) and inpatient-unit medical nurses were utilized for ED patient care; hospital units normally utilized for other medical or therapeutic purposes were transformed into ED patient rooms; and rooms normally used for only one patient were expanded to at least a capacity of 2.
Comparisons to other pandemics and epidemics
Annual influenza epidemics are estimated to affect 5–15% of the global population. Although most cases are mild, these epidemics still cause severe illness in people and 290,000–650,000 deaths worldwide every year. On average 41,400 people die of influenza-related illnesses each year in the United States, based on data collected between 1979 and 2001. In industrialised countries, severe illness and deaths occur mainly in the high-risk populations of infants, the elderly and chronically ill patients, although the H1N1 flu outbreak (like the 1918 Spanish flu
The 1918–1920 influenza pandemic, commonly known by the misnomer Spanish flu or as the Great Influenza epidemic, was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was ...
) differs in its tendency to affect younger, healthier people.
In addition to these annual epidemics, Influenza A virus strains caused three global pandemics during the 20th century: the Spanish flu in 1918, Asian flu
Asian may refer to:
* Items from or related to the continent of Asia:
** Asian people, people in or descending from Asia
** Asian culture, the culture of the people from Asia
** Asian cuisine, food based on the style of food of the people from Asi ...
in 1957, and Hong Kong flu
The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic whose outbreak in 1968 and 1969 killed between one and four million people globally. It is among the deadliest pandemics in history, and was caused by an H3N2 strain of ...
in 1968–69. These virus strains had undergone major genetic changes for which the population did not possess significant immunity
Immunity may refer to:
Medicine
* Immunity (medical), resistance of an organism to infection or disease
* ''Immunity'' (journal), a scientific journal published by Cell Press
Biology
* Immune system
Engineering
* Radiofrequence immunity desc ...
. Recent genetic analysis has revealed that three-quarters, or six out of the eight genetic segments, of the 2009 flu pandemic strain arose from the North American swine flu strains circulating since 1998, when a new strain was first identified on a factory farm in North Carolina, and which was the first-ever reported triple-hybrid flu virus.
The Spanish flu
The 1918–1920 influenza pandemic, commonly known by the misnomer Spanish flu or as the Great Influenza epidemic, was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was ...
began with a wave of mild cases in the spring, followed by more deadly waves in the autumn, eventually killing hundreds of thousands in the United States and 50–100 million worldwide. The great majority of deaths in the 1918 flu pandemic were the result of secondary bacterial pneumonia. The influenza virus damaged the lining of the bronchial tube
A bronchus is a passage or airway in the lower respiratory tract that conducts Atmosphere of Earth, air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the Carina of trachea, carina are the right ma ...
s and lungs of patients, allowing common bacteria from the nose and throat to infect their lungs. Subsequent pandemics have had many fewer fatalities due to the development of antibiotic medicines which can treat pneumonia.
The influenza virus has caused several pandemic threats over the past century, including the pseudo-pandemic of 1947 (thought of as mild because although globally distributed, it caused relatively few deaths), the 1976 swine flu outbreak
In 1976, an outbreak of the swine flu, influenza A virus subtype H1N1 at Fort Dix, New Jersey caused one death, hospitalized 13, and led to a mass immunization program. After the program began, the vaccine was associated with an increase in report ...
and the 1977 Russian flu
The 1977 Russian flu was an influenza pandemic that was first reported by the Soviet Union in 1977 and lasted until 1979. The outbreak in northern China started in May 1977, slightly earlier than that in the Soviet Union. The pandemic mostly affe ...
, all caused by the H1N1 subtype. The world has been at an increased level of alert since the SARS
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sever ...
epidemic in Southeast Asia (caused by the SARS coronavirus
Severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1; or Severe acute respiratory syndrome coronavirus, SARS-CoV) is a strain of coronavirus that causes severe acute respiratory syndrome (SARS), the respiratory illness responsible for th ...
). The level of preparedness was further increased and sustained with the advent of the H5N1 bird flu outbreaks because of H5N1's high fatality rate, although the strains currently prevalent have limited human-to-human transmission ( anthroponotic) capability, or epidemicity.
People who contracted influenza before 1957 appeared to have some immunity to H1N1 flu. According to Daniel Jernigan, head of flu epidemiology for the U.S. CDC "Tests on blood serum from older people showed that they had antibodies that attacked the new virus ... That does not mean that everyone over 52 is immune, since Americans and Mexicans older than that have died of the new flu".
In June 2012, a model based study found that the number of deaths related to the H1N1 influenza may have been fifteen times higher than the reported laboratory confirmed deaths, with 80% of the respiratory and cardiovascular deaths in people younger than 65 years and 51% occurring in southeast Asia and Africa. A disproportionate number of pandemic deaths might have occurred in these regions and that efforts to prevent future influenza pandemics need to effectively target these regions.[, citing ]
A WHO-supported 2013 study estimated that the 2009 global pandemic respiratory mortality was ~10-fold higher than the World Health Organization's laboratory-confirmed mortality count (18.631). Although the pandemic mortality estimate was similar in magnitude to that of seasonal influenza, a marked shift toward mortality among persons less than 65 years of age occurred, so that many more life-years were lost. Between 123,000 and 203,000 pandemic respiratory deaths were estimated globally for the last nine months of 2009. The majority (62–85%) were attributed to persons under 65 years of age. The burden varied greatly among countries. There was an almost 20-fold higher mortality in some countries in the Americas than in Europe. The model attributed 148,000–249,000 respiratory deaths to influenza in an average pre-pandemic season, with only 19% in persons <65 years of age.
The ongoing COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...
is not caused by an influenza virus but SARS-CoV-2
Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...
, a coronavirus which also primarily affects the respiratory system. As of this pandemic had more than confirmed cases worldwide, and over associated deaths.
See also
* SARS
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sever ...
* 2009 swine flu pandemic tables
* 2015–16 Zika virus epidemic
* Black Death
The Black Death (also known as the Pestilence, the Great Mortality or the Plague) was a bubonic plague pandemic occurring in Western Eurasia and North Africa from 1346 to 1353. It is the most fatal pandemic recorded in human history, causi ...
* COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...
* G4 EA H1N1
In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the Spanish flu, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus ...
* Health crisis A health crisis or public health crisis is a difficult situation or complex health system that affects humans in one or more geographic areas (mainly occurred in natural hazards), from a particular locality to encompass the entire planet. Health cri ...
* MERS
Middle East respiratory syndrome (MERS) is a viral respiratory infection caused by ''Middle East respiratory syndrome–related coronavirus'' (MERS-CoV). Symptoms may range from none, to mild, to severe. Typical symptoms include fever, cough, ...
* Public health emergency (United States)
In the United States, a public health emergency declaration releases resources meant to handle an actual or potential public health crisis. Recent examples include:
* Incidents of flooding
* Severe weather
* the 2009 swine flu pandemic, which Hom ...
* Western African Ebola virus epidemic
The 2013–2016 epidemic of Ebola virus disease, centered in Western Africa, was the most widespread outbreak of the disease in history. It caused major loss of life and socioeconomic disruption in the region, mainly in Guinea, Liberia and S ...
References
Further reading
*
*
*
*
*
External links
*
Pandemic (H1N1) 2009
at the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO)
International Society for Infectious Diseases
PROMED-mail news updates
H1N1 Flu Resource Centre
of The Lancet
''The Lancet'' is a weekly peer-reviewed general medical journal and one of the oldest of its kind. It is also the world's highest-impact academic journal. It was founded in England in 1823.
The journal publishes original research articles, ...
Novel H1N1 Influenza (Swine Flu) Overview
from CIDRAP
The Center for Infectious Disease Research and Policy (CIDRAP) is a center within the University of Minnesota that focuses on addressing public health preparedness and emerging infectious disease response. It was founded in 2001 by Dr. Michael Os ...
Influenza Research Database
Dean Julio Frenk, 2009-09-17
EU response to influenza
2009 influenza A (H1N1) pandemic
European Centre for Disease Prevention and Control
The European Centre for Disease Prevention and Control (ECDC) is an agency of the European Union (EU) whose mission is to strengthen Europe's defences against infectious diseases. It covers a wide spectrum of activities, such as: surveillance, e ...
(ECDC).
Summaries of the pandemic
European Centre for Disease Prevention and Control
The European Centre for Disease Prevention and Control (ECDC) is an agency of the European Union (EU) whose mission is to strengthen Europe's defences against infectious diseases. It covers a wide spectrum of activities, such as: surveillance, e ...
(ECDC).
European Commission—Public Health
EU coordination on Pandemic (H1N1) 2009.
UK National Pandemic Flu Service
Official UK government information on swine flu
from Directgov
Directgov was the British government's digital service for people in the United Kingdom, which from 2004 provided a single point of access to public sector information and services. The site's portal was replaced (along with the Business Link po ...
Human/Swine A/H1N1 Influenza Origins and Evolution
Health Canada flu portal
Pan-American Health Organization (PAHO) Swine Influenza portal
H1N1 Influenza (Flu) portal
at the US Centers for Disease Control (CDC)
US Government swine, avian and pandemic flu portal
{{Good article
2009 disease outbreaks
2010 disease outbreaks
21st-century epidemics
Influenza A virus subtype H1N1
Influenza pandemics
Public health emergencies of international concern