New sero survey shows 1 in 4 exposed to Covid-19 in Delhi

The report also showed that a large proportion (43.5%) of people who had previously been diagnosed with Covid-19 remained sero-negative.

Around one in four of the 15,000 people tested in the latest serological survey in the capital showed prevalence of antibodies against Sars-Cov-2, the government informed the Delhi high court on Wednesday, indicating that the proportion of people with antibodies has remained largely unchanged from the previous round of the exercise.

A man gives a swab sample for coronavirus testing in Govindpuri, New Delhi.(Biplov Bhuyan/HT PHOTO)

The report also showed that a large proportion (43.5%) of people who had previously been diagnosed with Covid-19 remained sero-negative, a statistic that independent experts said underlined how such surveys were underestimating how many people had been exposed.

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Authors of the report, however, said it was because antibodies take time to develop after contracting an infection and that they remain detectable only for a limited period.

Researchers caution that absence of antibodies in infected people cannot be conclusive evidence that they are unprotected from the disease.

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Equally, it isn’t clear how long and how strong a protection against Covid-19 such antibodies can offer. The prevalence of the antibodies among those sampled in the fourth round of the sero survey has gone up by minuscule 0.4 percentage points in a month-and-a half – from 25.1% in the first week of September to 25.5% in the third week of October. The authors of the study attributed the lack of an increase of sero-prevalence to “fewer infections reported in August” and “disappearing” antibodies.

The findings of the October round of sero-prevalence survey report were submitted during the hearing in the Delhi high court on a plea seeking more aggressive testing in Delhi. During the hearing, the court censured the government for relaxing norms for public movement at a time when infections have “spiralled alarmingly”. The court asked the government to put in place a policy on controlling the “mind-boggling” rate of new cases. “No household has been left untouched,” a bench of justice Hima Kohli and justice Subramonium Prasad said.

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“The rates in the city are mind-boggling. The number of deaths is in double figures every day. What’s with the Delhi government allowing all the un-lockdown when the cases are skyrocketing? Why have you opened everything? What are the strategies that you are following?” the court said.

“Today, Delhi is beating the whole state of Maharashtra and Kerala hands down in Covid-19 infections. When the numbers are decreasing in all the states, then why numbers are rising only in your state? Either there is no control or there is lack of control,” the bench said.

The seven-day average of daily new cases in Delhi has touched 7,148, and the Union territory has seen an average of 75 Covid-19 deaths a day over the past week. Delhi currently accounts for the most daily cases in the country. And there are no Covid-19 beds available in private hospitals.

In June-end , 22.6% of the 21,000 people sampled had antibodies. This proportion shot to 29.1% among the 15,000 people sampled in August, and then dropped to 25.1% among the 17,000 people sampled in September.