Serial Interval and Covid-19

• 17 Sep 2020

Why in News

According to a recent research paper “Serial Interval of SARS-CoV-2 was Shortened Over Time by Non-pharmaceutical Interventions”, China was able to contain Covid-19 due to its ability to manage the serial interval.

• China has now gone over a month without any locally transmitted Covid-19 cases.

Key Points

• Serial Interval:
  
  • It 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.
  • Origin: 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 UK during 1942-45.
    
    • Later, another British physician RE Hope Simpson used the term serial interval, defining it as the interval between successive illness onsets.
  • The serial interval depends on other epidemiological parameters such as the incubation period and the reproduction rate or R nought.
    
    • The incubation period is the time between a person’s exposure to the virus and symptom onset.
    • The reproduction rate is the number of people who will be infected by one infected person.
• Contribution in Controlling Covid-19:
  
  • 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 people 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.
• Examples of China and South Korea:
  
  • The serial interval in Wuhan (China) came down from 7.8 days to 2.6 days between early January and early February. Quarantining contacts within 1 day from symptom onset helped reduce the transmission by 60%.
  • The serial interval in South Korea was estimated to be 3.63 days.
  • Both countries put a lot of emphasis on aggressive contact tracing, quarantine, and isolation, thereby ensuring that infected patients could not infect any more people later in the infection cycle.
  • Interventions such as suspension of intra- and inter-city travel, and different forms of social distancing widely implemented also kept the serial interval low.

Source: IE