Sero survey: A fifth of Indians infected, a third in urban slums

A little over a fifth of India’s population is infected with Covid-19, the latest sero survey released by ICMR reveals. The number is as high as a third in the case of urban slums and about a fourth for medical personnel across the country.

The last sero survey, conducted between August and September 2020, had put the ratio at 6.6%, and the very first one, in June last year, had put the number at 0.7%.

In terms of the number of people infected, while one crore persons were infected in June, this rose to 9 crore in September and to just under 30 crore today.

A few days ago, another sero survey, conducted for Delhi, indicated that over half the population had been infected.

While some have used this to argue that Delhi is reaching ‘herd immunity’, as a result of which the spread of the infection will slow dramatically, this is incorrect and health authorities continue to stress the need to wear masks and observe social distancing.

Yet, there is little doubt the results are encouraging. If nearly 30 crore persons are infected, but the RT-PCR and RAT tests are showing a much lower 1.08 crore number of infected persons, this means most of those infected are able to shrug off the disease without any kind of treatment.

Based on the second sero survey, the fatality rate was 0.09%; while 9 crore persons were infected, the number of deaths was 89,000. This number has now come down to 0.05% with 29.5 crore infected persons and 1.5 lakh deaths.

While under a fifth of people living in rural areas are infected, as per the latest sero survey – versus 26.2% in urban non-slums – the survey makes it clear rural areas have witnessed a faster rise in the infected population. Compared with the last survey, the infected population has jumped 4.3 times in rural areas versus 3.2 times in non-slum urban areas and 2 times in urban slums.

A puzzling aspect of the survey is the infection ratios among the young and the old. Children have the highest level of infection while it was previously believed they were the least likely to be infected. The infection rate for those between 10 and 17 was 25.3%, for those between 18 and 44 it was 19.9% and for those older than 45, it was 23.4%.

More worrying, the sero survey makes it clear the testing strategy is faulty. As per the sero survey, 21.5% of Indians are infected as they have antibodies. Yet the testing data is detecting a much smaller number of infections.

If you assume antibodies last six months, you need to see how many tests were done since August and what share of these persons were shown to be Covid-positive. A total of 17.6 crore tests were done in the last six months and 88 lakh persons were reported to be positive; that’s a ratio of around 5% versus the 21.5% thrown up by the sero survey.