The serial interval in the

epidemiology 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 evide ...

of communicable (infectious) diseases is the time between successive cases in a chain of transmission. The serial interval is generally estimated from the interval between clinical onsets (if observable), in which case it is the 'clinical onset serial interval'. It could in principle be estimated by the time interval between infection and subsequent transmission. If the typical time from the first person's clinical onset to when they infect another is ''TA'', and the incubation period of a subsequent case is ''IB'', then the clinical onset serial interval is ''TA + IB''. More realistically, the calculation would use the observed frequency distribution of times from onset of a single primary case to that of its associated secondary cases. If the distribution of timing of transmission events during the infectious period is not skewed around its mean, then the average serial interval is calculated as the sum of the average latent period (from infection to infectiousness) and half the average infectious period. Serial intervals can vary widely, especially for lifelong diseases such as

HIV infection Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual ma ...

, chickenpox, and

herpes Herpes simplex is a viral infection caused by the herpes simplex virus. Infections are categorized based on the part of the body infected. Oral herpes involves the face or mouth. It may result in small blisters in groups often called cold ...

. The serial interval for

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, ''seve ...

was 7 days. For the original strain of

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease quickly ...

, a 2020 review of the published literature shows its serial interval to be 4-8 days. Related but distinct quantities include the 'average transmission interval' sum of average latent and infectious period, the '

incubation period Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the in ...

' between infection and disease onset, and the 'latent period' between infection and infectiousness.

References

Epidemiology {{infectious-disease-stub