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Prevalence of Covid antibodies highest in urban slums: ICMR's second national serosurvey

India Today logo India Today 26-11-2020 India Today Web Desk
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ICMR has published the findings of its second national serosurvey which indicates that nearly 7 per cent of India's population (1 in 15 individuals) aged ten and above was exposed to the novel coronavirus, amounting to 7.4 crore infections till August.

The findings also suggest that one in nine individuals who did not report any Covid-19 symptoms in the past were found to be with SARS-CoV-2 antibodies.

Published in the Lancet Global Health pre-print, the findings state, "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. While this threshold is unknown, most estimates place it above 50 per cent."

In addition, the Indian Council of Medical Research's second national serosurvey also reveals that seroprevalence or the level of Covid-19 antibodies in a population is highest in urban slum areas followed by urban non-slum and rural areas. This further indicates asymptomatic seroconversion among the general population.

"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 findings went on to add.

The second national serosurvey also suggests that adult seroprevalence in India increased as much as ten times between May and August 2020. The published findings say, "Lower infection to case ratio in August compared to May reflects a substantial increase in testing across the country."

The findings also highlighted the need for nonpharmaceutical interventions, expecting transmissions to increase in rural areas in the coming months.

As many as 3,135 people tested for the presence of IgG antibodies against Covid-19 out of the 29,082 samples collected by ICMR. This amounts to an unweighted seroprevalence of 10·8 per cent. Out of these 29,082 individuals surveyed from August 17 to September 22, 6.6 per cent were found with past exposure to Covid-19. The findings, meanwhile, put seroprevalence among adults at 7.1 per cent.

ICMR conducted the first round of its national serosurvey in May 2020 when it reported that 82-131 infections were reported per case diagnosed as compared to 26-32 in August this year. For both of these serosurveys, the ICMR collected samples from the same 700 villages and wards from 70 districts across the country.

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