29% of Delhi has antibodies for COVID-19: Sero-survey

Antibodies against COVID-19 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.

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

"In the previous survey, it was found that over 22 per cent people had developed antibodies. Now, the August survey shows it is 29.1 per cent, meaning they had got infected and recovered," Jain said.

The minister also said that prevalence of antibodies found in males was 28.3 per cent, and in females 32.2 per cent in the latest survey.

The previous sero-prevalance survey done from June 27 to July 10 by the Delhi government in association with the National Centre for Disease Control, had used 21,387 samples and found that around 23 per cent of the people surveyed had an exposure to the novel coronavirus.

"The rise, rather than the exponential rise is not there. So, people are taking safety precautions it seems. But, we cannot afford to be be complacent and lower our guard, even though positivity rate at present is 7 per cent," Jain said.

The exercise was undertaken in the first week of August for a comprehensive assessment of the COVID-19 situation in Delhi and to formulate strategies based on its findings.

About 15,000 samples were collected as part of this exercise, spanning different areas and age groups, gender and economic class, he said.

Representative samples were taken from all the eleven districts.

Out of total number of samples, 25 per cent were taken from the age group of less 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 prevalance 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 prevalance was of 25 per cent compared to the last survey. In the August survey, 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 prevalance 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.

"Sero-prevalence of antibodies found in 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 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 infection. Also, experts says, herd immunity is said to have been built in 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 4,235.

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

Asked if opening of shops and malls in the city could lead to increase in cases, he said, this exercise has shown that the 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 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.

These T-cells, also called memory cells 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 heath bulletin of the Delhi health department.

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