Context: 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.

What is ‘serial interval’? 

• 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. 

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. 

How did China and South Korea manage the serial interval? 

• In the paper, the researchers found that the serial interval in Wuhan 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 Covid-19 transmission by 60 per cent, the researchers said. 
• This, the researchers suggest, was made possible due to aggressive contact tracing, quarantine, and isolation, thereby ensuring that infected patients, because they were isolated, could not infect any more people later in the infection cycle. 
• The report also mentioned that interventions such as suspension of intra- and intercity travel, and different forms of social distancing widely implemented in different Chinese cities kept the serial interval low. 
• Similarly, a separate study by researchers in Zurich and Seoul, published in the International Journal of Infectious Diseases, found that the serial interval in South Korea, another country whose Covid-19 response has been touted as a success story, was estimated to be 3.63 days, crediting the effectiveness of the country’s intensive contact tracing efforts.

Additional Facts
About the term Incubation Period

• The term incubation period refers to the time taken for the symptoms of a particular infection to appear in a person after exposure to the virus i.e. time lapse between the exposure and the first sign of the disease. This of importance to the health workers to carry out the disease prevention, control and quarantine processes.

Incubation Period of SAS CoV 2

• The incubation period of the new coronavirus could range anywhere between 2 to 14 days according to the Centre for Disease Control. The recent studies suggest that majority of the cases have an incubation period of 5 days.

Latency Period

• The term latency period is different from incubation period. Latency period is the time lapse between the infection and infectiousness. While some diseases are not infectious during the incubation period, diseases like COVID-19 are. The COVID-19 patients may spread the virus even during the incubation period and hence more difficult to control.