The first national population-based serosurvey has indicated that 0.73 per cent of adults in India were exposed to coronavirus, amounting to 6.4 million infections in all by early May 2020.

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.

ICMR’s serosurvey report suggests India may have exceeded the official US tally.

The findings of the serosurvey conducted by Indian Council of Medical Research (ICMR) were published in the Indian Journal of Medical Research. The report found that the seroprevalence ranged between 0.62 per cent and 1.03 per cent across four strata of districts--from zero to high level of cases.

A total of 30,283 households were visited in 700 clusters across 70 districts in the four strata.

“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 survey conducted between May 11 and June 4 testing 28,000 individuals by Covid Kavach ELISA antibody test warned that low prevalence observed in most districts indicates that India is in the early phase of the epidemic 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 the prioritization of testing among symptomatics or the variability in testing rates across the States.”

On May 18, India’s official count for coronavirus cases had crossed the hundred-thousand mark.

The survey pointed that the males living in urban slums and occupation with high risk of exposure to potentially infected persons were associated with seropositivity.

The seropositivity was the highest in the age group of 18-45 years (43.3 per cent), followed by those between 46-60 years (39.5 per cent). It was the lowest among those aged 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.

ICMR has recommended further national and local serosurveys are to better inform the public health strategy for containment and mitigation of the epidemic in various parts of the country.

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 laboratory was not available at the district headquarters and the samples were transported to the State headquarter hospitals for diagnosis, the survey found.

ICMR said in its report 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. 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.