Vaccine resistance is the evolutionary adaptation of pathogens to infect and spread through vaccinated individuals, analogous to antimicrobial resistance. It concerns both human and animal vaccines. Although the emergence of a number of vaccine resistant pathogens has been well documented, this phenomenon is nevertheless much more rare and less of a concern than antimicrobial resistance. Vaccine resistance may be considered a special case of

immune evasion Antigenic escape, immune escape, immune evasion or escape mutation occurs when the immune system of a host, especially of a human being, is unable to respond to an infectious agent: the host's immune system is no longer able to recognize and elimi ...

, from the immunity conferred by the vaccine. Since the immunity conferred by a vaccine may be different from that induced by infection by the pathogen, the immune evasion may also be easier (in case of an inefficient vaccine) or more difficult (would be the case of the universal flu vaccine). We speak of vaccine resistance only if the immune evasion is a result of evolutionary adaptation of the pathogen (and not a feature of the pathogen that it had before any evolutionary adaptation to the vaccine) and the adaptation is driven by the selective pressure induced by the vaccine (this would not be the case of an immune evasion that is the result of genetic drift that would be present even without vaccinating the population). Some of the causes advanced for less frequent emergence of resistance are that * vaccines are mostly used for prophylaxis, that is before infection occurs, and usually act to suppress the pathogen before the host becomes infectious * most vaccines target multiple

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

ic sites of the pathogen * different hosts may produce different immune responses to the same pathogen For diseases that confer long lasting immunity after exposure, typically

childhood diseases The term childhood disease refers to disease that is contracted or becomes symptomatic before the age of 18 or 21 years old. Many of these diseases can also be contracted by adults. Some childhood diseases include: Diseases from three years to ...

, it was argued that a vaccine may provide the same immune response as natural infection, so it is expected that there should be no vaccine resistance. If vaccine resistance emerges the vaccine may retain some level of protection against serious infection, possibly by modifying the immune response of the host away from immunopathology. The best known cases of vaccine resistance are for the following diseases * animal diseases **

Marek's disease Marek's disease is a highly contagious viral neoplastic disease in chickens. It is named after József Marek, a Hungarian veterinarian who described it in 1907. Marek's disease is caused by an alphaherpesvirus known as "Marek's disease virus" ( ...

where actually more virulent strains emerged after vaccination because the vaccine did not protect against infection and transmission, only against serious forms of the disease ** ''

Yersinia ruckeri ''Yersinia ruckeri'' is a species of Gram-negative bacteria, known for causing enteric redmouth disease Enteric redmouth disease, or simply redmouth disease is a bacterial infection of freshwater and marine fish caused by the pathogen ''Yersinia ...

'' because a single mutation was sufficient to generate vaccine resistance **

avian metapneumovirus Avian metapneumovirus (aMPV), also known as turkey rhinotracheitis or swollen head syndrome, causes a variety of disease syndromes in birds, depending on the bird species and virus type (A, B, C or D). First detected in 1978 in South Africa, the ...

* human diseases ** '' Streptococcus pneumoniae'' because recombination with another

serotype A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their surface antigens, allowing the epi ...

not targeted by the vaccine ** hepatitis B virus because the vaccine targeted a single site formed by 9 amino acids ** ''

Bordetella pertussis ''Bordetella pertussis'' is a Gram-negative, aerobic, pathogenic, encapsulated coccobacillus of the genus ''Bordetella'', and the causative agent of pertussis or whooping cough. Like '' B. bronchiseptica'', ''B. pertussis'' is motile and expres ...

'' because not all serotypes were targeted and later because acellular vaccines targeted only a few antigens Other less documented cases are for avian influenza,

avian reovirus Avian orthoreovirus, also known as avian reovirus, is an orthoreovirus from the Reoviridae family. Infection causes arthritis and tenosynovitis in poultry. It can also cause respiratory disease. Avian orthoreovirus infection is more common in yo ...

, ''

Corynebacterium diphtheriae ''Corynebacterium diphtheriae'' is the pathogenic bacterium that causes diphtheria. It is also known as the Klebs–Löffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834–1912) and Friedrich Löffl ...

'', feline calicivirus, ''

H. influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria ...

'',

infectious bursal disease virus An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

, '' Neisseria meningitidis'',

Newcastle disease virus Newcastle usually refers to: *Newcastle upon Tyne, a city and metropolitan borough in Tyne and Wear, England *Newcastle-under-Lyme, a town in Staffordshire, England *Newcastle, New South Wales, a metropolitan area in Australia, named after Newcastle ...

, and

porcine circovirus Porcine circovirus (PCV) is a group of four single-stranded DNA viruses that are non-enveloped with an unsegmented circular genome. They are members of the genus '' Circovirus'' that can infect pigs. The viral capsid is icosahedral and approxim ...

type 2.

References

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