Amy Kazmin in New Delhi
A new seroprevalence study in India’s southern state of Tamil Nadu has estimated that 31.6 per cent of the 72m residents have been exposed to the virus that causes Covid-19.
The results highlighted how the pathogen has spread far wider than New Delhi officially acknowledges.
India has reported 10.8m coronavirus cases among its 1.4bn people — the world’s second highest tally, after the US — and about 154,000 deaths.
Tamil Nadu, the country’s second most populous state, has reported more than 800,000 infections and 12,000 deaths.
But public health experts said India’s reported case count understates how widely the virus has spread among the population. A nationwide seroprevalence study released by the Indian Council of Medical Research last week estimated that one in five Indians had been exposed to the virus by early January.
The study in Tamil Nadu, carried out between mid-October and late November by the state government and the IDFC Institute, tested 26,640 adults from a representative sample of the population for the presence of antibodies that would indicate past infections caused by the Sars-CoV-2 virus.
The study found wide regional variations in seroprevalence across the state, with the rate as high as 51 per cent in some districts and just 11 per cent in the sparsely populous region of The Nilgiris.
Overall, seroprevalence in urban areas was higher, at 37 per cent, than in rural areas, with 27 per cent.
The study also found seroprevalence was significantly higher in working age people than among the elderly, with those over 75 years having an infection rate of just 25 per cent.
The study implied that at least 22.6m people in Tamil Nadu have been infected with Sars-CoV-2 by November, roughly 36 times the number of reported cases.