Explained | How will the ICMR sero survey aid the Covid-19 fight?

Sero surveys give us a better idea of how many people have actually been infected

The Indian Council of Medical Research (ICMR) has said it will conduct a fourth serological survey (sero survey) throughout the country to figure out what proportion of the population had been infected with Covid-19.

Sero surveys are tools that help scientists uncover the true extent of the virus’ spread in the population and could lay bare the actual impact of the second Covid wave in the country.

What is a sero survey?

Sero surveys serve to determine what percentage of a population has caught an infection, which is Covid-19 in this case, and also includes those who recovered from it. Sero surveys usually try to examine how much of the population has an antibody specific to the disease and its concentration, revealing hidden infections and aiding in pinning down the actual extent and prevalence of a disease.

How is a sero survey carried out?

In these studies, the blood serum of random and anonymous samples is tested with an antibody or serology test to see if an individual’s immune system has responded to the infection.

Sero surveys are generally targeted towards detecting the presence of the Immunoglobulin G (IgG) antibody, which develops two weeks after the onset of the infection and stays in the body for a long period of time.

Why do we need sero surveys?

Sero surveys give scientists, policymakers and the general public a better idea of how many people have been actually been infected by a disease. They not only take into account more than officially reported cases, but also reveal many asymptomatic or unreported cases that have flown under the radar.

They give a rough idea of how many people have actually contracted the infection and how far a community is from the elusive idea of herd immunity, which would require antibodies to be present in 60 to 70 per cent of a community’s population, according to experts.

What has the sero survey shown so far?

The first part of the study, conducted in May, compiled data from 65 out of 83 districts across India. It showed that 0.73 per cent of the population surveyed displayed evidence of past exposure to the novel coronavirus, according to ICMR.

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