Editor's Pick: reading into the sero survey

(The Editor's Pick is a new newsletter from The Hindu that provides a snapshot of the most important stories from today's edition of our newspaper, along with a note from our top editors on why we chose to give prominence to these stories.)

The third serological survey by the Indian Council for Medical Research has found that about one in five Indians were infected by the coronavirus till December 2020. Specifically, it found a prevalence of 21.5% in the samples surveyed across 70 districts in 21 States. This translates to about 270 million infected Indians, compared to the 10 million officially confirmed cases so far.

Serological surveys look for the presence of antibodies in the serum, or the liquid part of a person's blood. The presence of antibodies indicate that the person had been infected in the recent past, even though the virus itself may no longer be present in the body. The latest survey, conducted between December 17 and January 8, is the third to be undertaken pan-India since the pandemic broke out. The other two, conducted in May-June and August-September last year had found a prevalence of 0.7% and 7.1% respectively. The latest results show that the prevalence has jumped about three times since the previous survey. However, India has shown a decline in the number of daily reported cases since September.

The setting with the one of the highest prevalence as per the latest survey was urban slums, with 31%. It also found a prevalence of 25% in the 10-17 age group, debunking the theory that children and young adults were better protected.

While the latest survey shows a steep rise in the prevalence, there are experts who say that it is a vast underestimation and that the actual number could be as high as 50%. Eminent virologists T Jacob John and M.S. Seshadri, writing in The Hindu in November, had said that in asymptomatic or mild cases, the antibodies could disappear from the blood in 2 months or less. As per their estimation, such cases constitute about 80% of all infections.

While there may be disagreement on the numbers, the survey indicates that the epidemic continues its run in the community, and that the falling number of reported infections is no reason to let our guard down. This is what makes the story important.

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