While the COVID-19 case fatality rate (CFR) is roughly 5-6 percent, researchers think the infection fatality rate (IFR) is probably very low (under 0.1 percent), based on the antibody serosurveillance data and records from BMC on reported deaths.
Around 65 per cent of Mumbai's 12 million people live in the cramped, airless slums, making for easy transmission of the disease.
More than half of residents living in Mumbai's crowded slums may have contracted coronavirus and are likely being infected at a much higher rate than those not living in slum areas, a new study has found.
"The first round report of Sero Surveillance for Covid-19 infection in Mumbai indicates that 57 per cent of slum population and 16 per cent of non-slum population have developed antibodies".
"The results showed how crowding plays a key role in the spread of the infection", Dr Sandeep Juneja of Tata Institute of Fundamental Research (TIFR) told the BBC.
The survey also found that more women than men had developed antibodies.
The BMC claimed that higher prevalence in slums could possibly be due to the population density and shared common facilities like toilets and water points, the release said.
Infection fatality rate is different from cases fatality rate, which records deaths as a percentage of all confirmed positive cases, which have been clinically diagnosed through RT-PCR/antigen test. Planned repeat surveys will provide information about infection spread in both slums and non-slums, and could inform about herd immunity.
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Mumbai on Tuesday reported just 717 cases, the lowest figure in three months, while 2,467 patients were discharged, reducing the number of active cases to 20,251, according to the BMC.
Researchers have inferred from their findings that a high proportion of all infections are likely to be asymptomatic.
"This is a surprise, more people remain asymptomatic than we expected", said Suresh Kakani, Additional Municipal Commissioner. "Are we closer to herd immunity?"
Scientists believe the sample tested was "statistically robust" and representative.
Earlier this month a government survey found that almost one in four residents in India's capital, Delhi, has been exposed to coronavirus infection.
A serological survey involves testing of blood serum of individuals to check for the prevalence of antibodies against an infection.
Bhubaneswar: As many as 215 people tested positive for Covid-19 in Bhubaneswar Municipal Corporation (BMC) area of Odisha in last 24 hours, officials said on Tuesday.