- The serial interval is the duration between symptom onset of a primary case and symptom onset of secondary cases (contacts) generated by the primary case.
- In simple terms, the serial interval is the gap between the onset of Covid-19 symptoms in Person A and Person B, who is infected by Person A.
- The term was first used by British physician William Pickles, who had initially referred to it as transmission interval with reference to a hepatitis epidemic in the United Kingdom during 1942-45.
- Later, another British physician RE Hope Simpson used the term serial interval, defining it as the interval between successive illness onsets.
- It depends on other epidemiological parameters such as the incubation period, which is the time between a person’s exposure to the virus and symptom onset, and the reproduction rate or R naught, the number of people who will be infected by one infected person.
    What does changes in serial interval indicate?
- The serial interval helps to gauge the effectiveness of infection control interventions besides indicating rising population immunity and forecast future incidence.
- Thus, the more quickly persons who contracted Covid-19 are identified and isolated, the shorter the serial interval becomes and cuts down opportunities for transmission of the virus.
- To manage serial interval, a robust system of contact tracing, quarantine, and isolation protocols should be in place.
