Sero survey in three Mumbai wards finds 40% exposed to virus

MUMBAI: A total of 57% individuals from slums and 16% from other residential areas in three wards were exposed to SarsCOV-2 and recovered silently, the sero survey conducted by the Brihanmumbai Municipal Corporation, as part of t he national study, has found. Individuals in both these groups were asymptomatic.

“Overall, we have observed that 40% of those surveyed, in both slums and residential areas, were infected with Covid-19, but recovered. None of those tested for sero survey had to undergo RT-PCR test, as they were asymptomatic,” s ai d Suresh Kakani, additional commissioner, BMC. “The prevalence of the virus in slums is high due to densely populated areas. In non-slums (residential areas), better social distancing and maintenance of hygiene helped stop the spread to a large number of people,” said Kakani.

On July 3, the civic body, in collaboration with NITI-AAYOG and Tata Institute of Fundamental Research, started sero surveillance, in which a group of individuals undergo blood tests to detect the presence of Immunoglobulin-g (IGG) antibodies. IGG antibodies are produced by the body’s immune system on being exposed to a virus.

A sero survey helps identify individuals who were previously infected with the virus and have now recovered. Although the estimated target was 10,000 blood samples, the ongoing monsoon restricted the collection process to 6,936 samples, said a health officer from BMC.

The civic body has also run an antibody test on 1,000 health

workers, results of which are pending.

BMC officials believe the infection fatality rate (IFR) is likely to be low, between 0.05% and 0.10%. It is lower than CFR, which considers only confirmed cases. “Results of the sero surveillance are promising because it shows that a large number of people have recovered from the virus with the help of their own immunity,” said Dr Om Srivastava, epidemiologist and member of the state’s Covid task force.

The results will be re-evaluated later to learn about development of herd immunity, when a large portion of a community (the herd) becomes immune. BMC will conduct another sero surveillance next month in the same three wards.