BMC confident of herd immunity after studies says 57% Mumbai slum population has developed antibodies

Mumbai: Buoyed by the results of sero-prevalence survey, in which 57 per cent people tested in Mumbai slums were found to have antibodies to COVID-19, the Brihanmumbai Municipal Corporation (BMC) hopes that herd immunity in Mumbai, at least in the slum pockets, can be attained soon.

Mumbai is the worst coronavirus-affected city in Maharashtra with over 1.20 lakh Covid-19 patients and over 6,200 deaths so far. Nearly 60 per cent population of the metropolis resides in the slums, a major hotspot of coronavirus.

The SARS-CoV2 sero-prevalance study was conducted by the BMC jointly with Niti Aayog and Tata Institute of Fundamental Research (TIFR) on almost 7,000 people in three civic wards in the city. According to the survey, 57 per cent of the people tested in slum pockets had antibodies to COVID-19 as against 16 per cent in non-slum pockets.

“These results will be valuable to learn more about herd immunity. Although it is still unclear what level of prevalence leads to herd immunity, findings indicate that at least in slums this could be attained sooner than later, if the immunity exists and persists in a significant proportion of the population. Herd immunity can be achieved when around 60 per cent of the population has been exposed to the virus,” said Dr Daksha Shah, BMC deputy executive health officer.

Herd immunity is the resistance to the spread of a contagious disease within a population that results when  a sufficiently high proportion of individuals are immune to the disease. The survey showed prevalence in women was marginally higher than in men, but the age-wise prevalence in the population was comparable in these wards. The BMC is planning to carry out a repeat survey in the same three wards in August to capture changes in prevalence rates.

“While the survey provided information on presence of neutralizing antibodies and risk factors on SARS-CoV2 infection, the planned repeat surveys will provide information about infection spread in both slums and non-slums and could inform about herd immunity,” said a BMC official.

The civic officials claimed that taking together the current prevalence, the effective containment efforts and active measures undertaken by the BMC to isolate symptomatic cases are expected to keep the infection fatality rate (IFR) very low in the city.

However, the BJP has raised a question mark over its claims. “While, this survey has said 57 and 16 per cent people in slums and non-slum areas respectively have already recovered from corona, a survey recently done by a private lab said that 25 per cent people in the city have also been found recovered. It means nearly 40 per cent Mumbaikars, whose immunity was better and who took necessary preventive measures, managed to beat the corona threat on their own. So what is the BMC’s achievement in this?” asked BJP leader Ashish Shelar.