More than half of residents in several of Mumbai’s slums may have been infected with coronavirus, a study has found, suggesting that the spread of Covid-19 in India could be far greater than previously thought. The study – commissioned by authorities in India’s financial capital, where 40 percent of the population lives in slums –   surveyed 6,936 people for antibodies indicating past exposure to the virus.

It found that 57 percent of those in slums had antibodies, compared with 16 per cent of those residing in other parts of the city. The tests, which were conducted in the first half of July, also found a higher prevalence of antibodies among women than men. The findings add to evidence that the number of Covid-19 infections in India could be far greater than the official caseload, which is already the world’s third-highest. There have been almost 1.5m recorded infections and 33,000 deaths in the country.

Mumbai and the surrounding metropolitan region, home to about 20m people, has been hardest hit with more than 100,000 recorded cases and 6,000 deaths. The study indicates that social distancing and sanitation measures have failed to control the virus in Mumbai ‘s cramped settlements.

India’s government has controversially maintained that community transmission of the disease is not happening, a claim widely disputed by public health experts. India’s official death rate has, however, remained lower than in many other countries, including the UK. The Municipal Corporation of Greater Mumbai said its study implied a fatality rate of between 0.05 percent and 0.1 percent.

But public health experts fear that Indian authorities are underestimating the true number of deaths. Fatalities have been “higher than we think, without question”, said Ramanan Laxminarayan, founder of the Center for Disease Dynamics, Economics & Policy.

Modi stumbles India’s deepening coronavirus crisis. The implied fatality rate from the study “will extrapolate into an enormously large number” for Covid-19 infections across the country, pointed out Shahid Jameel, a virologist and chief executive officer of Wellcome Trust DBT India Alliance. Scientists have also cautioned that such studies need more analysis and scrutiny.