The first national serosurvey conducted by the Indian Council of Medical Research (ICMR), published in the Indian Journal of Medical Research, indicated that 6.4 million Indians were exposed to COVID-19 by early May.
The survey, conducted between May 11 and June 4, covered 28,000 individuals whose blood samples were tested for IgG antibodies using COVID Kavach ELISA kit.
The survey also found that while seropositivity was the highest in the age group of 18-45 years with 43.3 per cent, it was 39.5 per cent for those between 46-60 years and it was the lowest among those aged above 60 at 17.2 per cent.
Furthermore, while seropositivity was highest at 69.4 per cent in the rural areas, in urban slums it was 15.9 per cent and in urban non-slums, it was 14.6 per cent.
The survey estimated that India had a total of 64,68,388 adult infections by early May.
"The findings of our survey indicated that the overall seroprevalence in India was low, with less than one per cent of the adult population exposed to SARS-CoV-2 by mid-May 2020," the report said.
"The low prevalence observed in most districts indicates that India is in early phase of the epidemic and the majority of the Indian population is still susceptible to SARS-CoV-2 infection," it added.
The survey also pointed out that seropositivity being reported in districts with no cases could be due to low testing and poor access to the testing laboratories.
"The present findings of seropositivity in the strata of districts with zero to low incidence of COVID-19 cases underscore the need to strengthen surveillance and augment the testing of suspected cases in these areas," ICMR said.
The survey was carried out across 70 districts and categorised into four strata based on the incidence of reported COVID-19 cases. From 700 clusters in these districts, 30,283 households were visited. The report stated that seroprevalence ranged between 0.62 and 1.03 per cent across the four strata.
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