The third serological survey conducted by the Indian Council of Medical Research has found that more than one-fifth of the country’s adult population had at some point been infected by Covid-19 by mid-December. The separate data released on seroprevalence among those aged 10-18 was found to be 25.3%. The data released reflects the prevalence of antibodies, read as evidence that the person has had Covid-19. “Delhi was not a part of the survey. We have made statistical extrapolations so we can say that 21.4% of Indians were seropositive,” ICMR director general Balram Bhargava said. The third survey found a significant increase in prevalence among adults at 21.4%, up from 7.1% during the second survey in August. In the first survey conducted in April, only 0.7% prevalence was detected. It was conducted between December 17 and January 8. The latest survey was conducted in the same 700 villages in 70 districts across 21 states where the first and second rounds were conducted in April and August. Among healthcare workers, seroprevalence was 25.7%, with 26.6% among doctors and nurses.