29% in Delhi have developed antibodies, sero-survey shows

Antibodies against coronavirus infection have been found in 29.1 per cent of people in the latest sero-prevalence survey in the national capital, Delhi Health Minister Satyendar Jain said on Thursday.

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Interacting with reporters, he said, 15,000 representative samples were taken in the August 1-7 survey from 11 districts here, and the next exercise will begin from September 1.

Out of a total number of samples, 25 per cent were taken from the age group of fewer than 18 years, another 50 per cent from 18-49 years age bracket and remaining 25 per cent from those in the age group of 50 years or more, the Delhi health minister said.

The sero-prevalence found in North East district was 29 per cent, South district 27 per cent, South East 33 per cent and New Delhi 24 per cent, Jain said.

There has been an increase of 6 per cent to 50 per cent in the prevalence of antibodies among people in various districts compared to the prevalence found in different districts in the previous survey, he said.

Also, the average rise in prevalence was of 25 per cent compared to the last survey. In the August survey, the lowest rise was found in North East district, from 27.7 per cent (last survey) to 29 per cent (August survey), thus an increase of 6.7 per cent, Jain said.

Also, in South-East district, the rise in prevalence is from 22 per cent in the previous exercise to 33 per cent in the current one, an increase of 50 per cent, he said.

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"Sero-prevalence of antibodies found in the age group of less than 18 was 34.7 per cent, in 18-50 years 28.5 per cent, and 31.2 per cent in 50 years and above," Jain said.

The minister said, he had suggested taking a larger sample than used in the previous exercise, but scientists and experts at the Maulana Azad Medical College (MAMC) which led the team had decided to keep 15,000 as the representative sample size based on their assessment.

"The findings also mean that 71 per cent still have chances of getting an infection. Also, experts say, herd immunity is said to have been built in the community if 40-50 per cent or more develop antibodies, so we have to be still very watchful," he added.

Delhi recorded 1398 fresh coronavirus cases on Wednesday, taking the tally in the city to over 1.56 lakh, while the death toll from the disease mounted to 4235.

A sero-prevalence survey involves testing the blood serum of individuals to check for the prevalence of antibodies against infection.

Asked if the opening of shops and malls in the city could lead to increase in cases, he said, this exercise has shown that the rise has been of 25 per cent compared to the last time, so it could be 50 per cent increase next due to opening of businesses.

On the longevity of antibodies developed in response to Covid-19, he said, according to experts these antibodies can last for several months, say 5-8 months, but the body also produces T-cells in response to the infection.

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These T-cells also called memory cells to help fight any possible infection again, and so, it is "very rare" that a person who has recovered from Covid-19 will be diagnosed with it again.

The total number of tests done in Delhi till August 19 to diagnose Covid-19 stands at 13,58,189. The number of tests done per million, as on Wednesday was 71,483, according to the latest health bulletin of the Delhi health department.

On Wednesday, the number of containment zones stood at 560.

(With PTI inputs)