57% have had Covid-19 in Mumbai slums: Survey

The slum colonies of India’s financial capital, Mumbai, seem at the forefront of achieving herd immunity against the Covid-19 pandemic.

A fortnight-long study revealed that 57 percent of slum population and 16 percent of non-slum residents in three of the 24 civic wards of Mumbai had developed antibodies.

The indications came from a survey undertaken by the BrihanMumbai Municipal Corporation (BMC), NITI Aayog and Tata Institute of Fundamental Research (TIFR).

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As part of the survey – ‘Serological Surveillance for SARS-CoV2 Infection’, in the first round 6,936 samples out of the estimated 8,870 were collected from the three wards.

While the F/North ward covered Matunga, Sion and Wadala areas, M/West included Chembur and Tilak Nagar, and R/North comprised Dahisar and Mandapeshwar.

The Anti-SARS-CoV2-IgG antibodies were detected using Chemiluminescence assay (CLIA) by Abbott.

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The study was carried out – in the first fortnight of July - in collaboration with Kasturba Molecular Diagnostic Laboratory, Translational Health Science and Technology Institute, ATE Chandra Foundation and IDFC Institute – and it is the largest cross-sectional survey in India.

“Systematically conducted studies estimate around 57 per cent sero-prevalence in slums and 16 per cent in non-slums, on an average in the three wards, that were studied,” the BMC said in a press statement issued on Tuesday night.

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"First round report of sero surveillance for Covid-19 infection in Mumbai indicates that 57% of the slum population and 16 percent of the non-slum population developed antibodies. The infection fatality rate is very low. Are we closer to herd immunity?," BMC's additional municipal commissioner Ashwini Bhide tweeted.

The BMC press statement said: "The 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 at least in slums this could be attained sooner or later, if the immunity exists and persists in a significant proportion of the population."

The results suggest that asymptomatic infections are likely to be a high proportion of all infections.

The higher prevalence in slums could be possibly because of population density and common facilities like toilets and water points.

The BMC said relatively low prevalence in non-slums suggests that social distancing and related precautions such as wearing masks have been effective in slowing the infection spread.

As on July 28, Mumbai has recorded 1,10,846 COVID-19 cases and 6,184 deaths.