Third sero survey indicates that 21.5 per cent Indians exposed to virus; fourfold increase in rural areas

Published : Feb 05, 2021 10:04 IST

A doctor at Hamidia Hospital in Bhopal being administered the COVID-19 vaccine Covishield on January 28.

A doctor at Hamidia Hospital in Bhopal being administered the COVID-19 vaccine Covishield on January 28.

The results of the third sero surveillance survey conducted by the Indian Council of Medical Research (ICMR) between December 17, 2020 and January 8, 2021, has revealed that 21.4 per cent of the adult Indian population (≥18 years) developed antibodies to COVID-19, that is, showed exposure to the virus. This is a significant threefold rise from the 7.1 per cent that emerged from the second survey done between August 17 and September 22, 2020. This means that the number of Indians who have been infected has increased from the estimated 74.3 million in the second survey to around 225 million (22.5 crores) today. Significantly, this has happened in a period in which the daily cases had passed their peak and were heading steadily downwards.

The third sero survey reaffirmed what the previous ones showed, namely, the number of people infected was far higher that what testing for COVID-19 had thrown up. Thus, by January 8, the last day of the third survey, India had reported only 10.4 million cases confirmed by tests. The gap is not only huge, the ratio of actual to confirmed cases could in fact have become slightly larger between the second and third surveys. This also indicates that the testing rates have remained low and can scarcely explain the eventual transition to falling numbers.

The third sero-survey also showed that prevalence rates among Health Care Workers, at 25.7 per cent, was much higher compared to the general population. Among HCW, doctors reported higher rates of exposure to the virus (26.6 per cent) as compared to para medical staff, field and administration staff.

The third survey drew its samples from the same 700 villages/wards in 70 districts in 21 States involved in the previous two surveys. A comparison of the results of these rounds of surveys reveals not only the scale of the spread but also important changes in the pattern. In the second survey, prevalence was found to be greater in urban slums (16.6 per cent) than in non-slum areas (8.2 per cent), while in rural areas it was low (4.4 per cent). The degree of change in the third round has been highest in rural areas at 19.1 per cent, a more than fourfold rise. In non-slum urban areas, it was 26.2 per cent, a rise of a little over threefold, while in urban slums the prevalence had increased to 31.7 per cent. The infection has spread faster in population groups where the incidence was less earlier, thereby narrowing the variations in the degree of prevalence across groups.

The second survey had reported no significant variations in prevalence by age and gender. However, the third survey indicated that the exposure among children between 10 to 17 years of age, at 25.3 per cent, is higher than in the adult population. Among adults, the 18-44 years age group shows a sero prevalence of 19.9 per cent, while in the 45 to 60 and 60 years and above groups it is 23.4 per cent. Similarly, the prevalence rate among women, 22.7 per cent, is higher than the 20.3 per among men.

Population still vulnerable

In the media briefing, the Union Health Secretary was optimistic that the number of positive cases was only 1.68 lakh and that too on a declining trajectory. Forty-seven districts in the country did not report a single fresh case, while in 251 districts, no case of death was reported. However, the third sero survey results affirm the fact that the measures taken to control the infection have not stopped it from spreading far and wide in India. At the same time, the proportion of asymptomatic cases in them has turned out to be exceptionally high. Despite this large spread and falling number of reported cases, as the ICMR Director General stated in his presentation, a large proportion of the population still remained vulnerable. It was stressed that prevention was still the key and vaccines were necessary, apart from the use of masks and adherence to social distancing norms.

Vaccination targets

The number of people vaccinated in the nearly three weeks since the start of the programme, and that too with only their first dose, is only 4.5 million, a fraction of the number the sero survey shows to have already been exposed to the virus. It would appear to be a big challenge to ensure that the vaccine reaches the vulnerable population before the infection does. For that the rate of vaccination would need significant stepping up. To even cover the 30 crore people (health care and frontline workers and population above 50 years of age) who are initially to receive the vaccine, 600 million doses would have to be administered. At even two million a day, many times the average or maximum numbers attained so far, that would take 300 days or until the end of 2021. That could be enough time for the virus to reach the yet unexposed large population and perhaps result in a second wave, about which the World Health Organisation has also warned.

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