Nearly 7% of India’s population aged ten years and above was exposed to coronavirus infection by August 2020, with an estimated 74.3 million infections, indicated findings of the second nationwide serosurvey done by the Indian Council of Medical Research (ICMR). The findings published in the Lancet Global Health pre-print, said that nearly one in 15 individuals aged ten years and above had coronavirus infection by August 2020 and the adult seroprevalence increased 10 times between May and August 2020.The first nationwide serosurvey in India was conducted in May, when the entire country was under stringent lockdown, and indicated a low prevalence of 0·73% among the general adult population. The ICMR conducted a cross-sectional survey in the same 700 clusters (villages in rural areas and wards in urban areas) from 70 districts in 21 Indian states as in the first nationwide serosurvey between 17 August and 22 September 2020. Of the 29,082 individuals tested for the presence of IgG antibodies against coronavirus, 3,135 tested positive, with an unweighted seroprevalence of 10·8%. Of the 29,082 people (aged 10 and above) surveyed from August 17 to September 22, 6.6% showed evidence of past exposure to covid-19 while the seroprevalence among adults was 7·1%. The seroprevalence was similar across age groups, sex, and occupation, according to the paper. “The overall seroprevalence below 10% in India indicates that a large proportion of population remains susceptible to coronavirus infection. The transmission of infection is expected to continue in most Indian states till the herd immunity threshold is achieved, either by natural infection or vaccination,” the study said. The infection doubling time at the national level was estimated to be 27 days. Assuming the same rate of infection continues, the required herd immunity threshold might be achieved by November – December 2020, the study said. Further, one in nine individuals who did not report any covid-19-related symptoms in the past had the presence of SARS-CoV-2 IgG antibodies indicating asymptomatic seroconversion among the general population in India. Sero conversion was also documented among individuals without a history of known contact with a COVID-19 case, and among those without any prior SARS-CoV-2 testing. “Our data supports the expansion of testing strategies to include individuals without having known exposure or symptoms. We found only 3 per cent of seropositive individuals reported COVID-19 symptoms highlighting the limitations of symptom directed testing and the importance of universal prevention methods,” the report said. Seroprevalence was found to be highest in urban slum areas followed by urban non-slum and rural areas. While population density coupled with high mobility, and challenges in safe distancing and hand hygiene are the main drivers of spread of infection in urban areas, especially urban slums, the findings of the sero survey also indicate substantial transmission among the rural population now, in contrast to the first round, the report said.”Transmission will increase further in these rural areas in the coming months, underscoring the need for implementing nonpharmaceutical interventions as well as strengthening healthcare facilities for the effective management of cases,” it said. In combination with the first round of the national survey and other serosurvey data, a clear picture of India’s epidemic emerges with high prevalence in urban slums, affecting the remainder of their city, and now spilling over into the vast rural areas, the report said. While the epidemic was successfully contained to the cities at the outset, the current generalized trend portrays many forthcoming challenges, it said.