India may have crossed 6.4 mn cases in May, ahead of US: Serosurvey

ICMR report found seroprevalence in the 0.62-1.03% range across four strata of districts, from zero to high level of cases; 30,283 households were visited in 700 clusters across 70 districts

India may have had 6.4 million coronavirus cases by May, the first national population-based sero survey conducted by the Indian Council of Medical Research (ICMR) has indicated. The survey suggests that 0.73 per cent adults in India were exposed to coronavirus, amounting to 6.4 million infections by early May.

India is currently second in the world, with over 4.5 million reported cases, while the US has the highest number of around 6.4 million Covid-19 cases according to the John Hopkins Covid tracker. But ICMR’s sero survey report suggests India may have exceeded the official tally of the US.

The findings of the survey were published in the Indian Journal of Medical Research. The report found that the seroprevalence ranged between 0.62 and 1.03 per cent across the four strata of districts — from zero to high-level of cases. A total of 30,283 households were surveyed in 700 clusters in 70 districts.

“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 survey, conducted between May 11 and June 4, tested blood samples from 28,000 individuals by Covid Kavach ELISA antibody test, warned that the low prevalence observed in most districts indicates that India is in early phase of the pandemic and the majority of the Indian population is still susceptible to SARS-CoV-2 infection.

The report said: “The high infection to case ratio in India could be on account of prioritisation of testing among symptomatic persons or the variability in testing rates across the state.”

On May 18, India’s official count for coronavirus cases had crossed the 100,000 mark.

The survey pointed out that men living in urban slums and in occupations with a high risk of exposure to potentially infected persons were associated with seropositivity.

The seropositivity was the highest in the age group of 18 to 45 years (43.3 per cent), followed by those between 46 and 60 years (39.5 per cent). It was the lowest among those above 60 (17.2 per cent). Nearly half of the participants were aged between 18 and 45 and 51.5 per cent were females. In all, 18.7 per cent of the participants had an occupation with a high risk of exposure to potentially infected persons.

The survey said that there could be under-detection of Covid-19 cases in the zero stratum districts on account of low testing as well as poor access to the testing laboratories. In four of the 15 districts in such areas, Covid-19 testing laboratories were not available at the district headquarters, and the samples were transported to the state headquarter hospitals for diagnosis.

The ICMR said that seroprevalence estimates conducted later in the epidemic, or in the settings with higher prevalence, will provide more robust infection to case and infection to fatality ratios. Serosurvey involves collection of blood samples from a group of individuals to check them for antibodies for Covid-19. If the test is positive, it shows that the person has been infected in the past.

The survey while providing scientific guidance shows the percentage of people who are more at risk of catching the infection and points at the area which require more containment effort.