Delhi may be heading towards herd immunity against COVID-19, suggests fifth round of sero survey

‘50-60% of sample subjects have antibodies in one district’

January 25, 2021 10:44 pm | Updated 10:47 pm IST - New Delhi

An RT-PCR test being conducted at Sant Ravidas Nagar in north Delhi.

An RT-PCR test being conducted at Sant Ravidas Nagar in north Delhi.

The outcome of the fifth round of seroprevalence survey has indicated that Delhi population could be heading towards attaining herd immunity against COVID-19 infection, sources said on Monday.

The survey has found that in one district, 50-60% of the sample population have developed antibodies, they said.

For the survey, which ended a few days ago, samples of over 25,000 people from various districts across the city were collected, the sources said.

Delhi’s population is over two crore, spread across 11 districts.

Experts say herd immunity is said to have been developed in a population segment if 50-60% of those are found to have the presence of antibodies in a seroprevalence survey.

Herd immunity implies that in any set of people in a community, after becoming affected by the virus, a lot many of them become immune to it on account of antibodies developed in response to it. And, hence, such people become a protective layer between the infected person and the unaffected people, thereby breaking the chain of viral transmission.

This is the fifth such exercise that was conducted here, but the Delhi government has not given any official version on it.

The first seroprevalence survey, done from June 27 to July 10 by the Delhi government in association with the National Centre for Disease Control (NCDC), had used 21,387 samples and found that around 23% of the people surveyed had an exposure to the novel coronavirus.

The exercise in August showed 29.1% people had antibodies. Also, 79 of the 257 people who had tested positive and then recovered, and were part of the survey done in the first week of August, however, did not have the antibodies, according to a report released later.

In the survey in September and October, the figures stood at 25.1% and 25.5%.

The exercises were undertaken for a comprehensive assessment of the situation and to formulate strategies based on its findings.

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