What is Serial interval of COVID-19?

Since the COVID-19 outbreak, several epidemiological terms we came across regarding pandemic, and now they have become a commonplace. A research paper that was published recently in a Journal Science which is written by Benjamin Cowling and other researchers at the University of Hong Kong said China, where now over a month, not any locally transmitted COVID-19 cases have been found and China was able to contain COVID-19 due to its ability to manage the serial interval.

What is the Serial interval?

It is the duration time between the symptom of the onset of a primary case and symptom onset of secondary cases (contacts) that is generated by the primary case. Or for further understanding, we can say that the serial interval is the gap between the onset of COVID-19 symptoms in supposing Person A and Person B, who is infected by a Person B.

How the term Serial Interval was originated?

The term was first used by William Pickles, a British physician. During 1942-45, he initially referred to it as a transmission interval with reference to a hepatitis epidemic in the United Kingdom. Later, another British physician RE. Hope Simpson used the term as a serial interval and defined it as the interval between successive illness onsets.

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What do the researchers in their paper titled “Serial interval of SARS-CoV-2 was shortened over time by non-pharmaceutical interventions”, explained?

The researchers in their paper explained that the serial interval depends on other epidemiological parameters like the incubation period. It is the time between a person's exposure to the virus and symptom onset and the reproduction rate or R naught which is the number of people who will be infected by one infected person.

How serial interval can contribute to controlling COVID-19?

The serial interval helps to gauge the effectiveness of infection control interventions besides indicating rising population immunity and forecast future incidence.

Therefore, as soon as persons who contracted with COVID-19 are identified and isolated then shorter will be the serial interval and hence cuts down opportunities for the transmission of the virus. A robust system of contact tracing, quarantine, and isolation protocols should be used to manage serial interval.

Let us have a look at China and South Korea regarding serial interval.

Researchers in the paper told that the serial interval in Wuhan came down from 7.8 days to 2.6 days between early January and early February. Within 1 day, quarantining contacts from symptom onset helped to reduce COVID-19 transmission by around 60%.

As per researchers, this was made possible due to aggressive contact tracing, quarantine, and isolation. Also, they ensured that the infected patients who were isolated could not infect any more people later in the infection cycle. Further, they mentioned that interventions like suspension of intra and intercity travel and different forms of social distancing widely implement in several cities of China and kept the serial interval low.

Also, a separate study is also published in the International Journal of Infectious Diseases by the researchers in Zurich and Seoul. There, they found that the serial interval in South Korea was estimated to be 3.63 days which credited the country's intensive contact tracing efforts.

So, now you may have understood about serial interval and how it can be helpful in controlling or managing COVID-19.

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