How many cases has India really had?
Although I’ve given it a glorified name tongue-firmly-in-cheek, my estimation relies on the fact that there are more real cases than the official tally suggests. How many more? This depends on your level of cynicism: my Cynic-o-Meter starts at 10x and the default level is 20x. So, if the official number of cases across India is just over 10 million, the actual number is likely to be 200 million, or around 15 per cent of the population.
However, the Indian Council of Medical Research (ICMR)’s own seroprevalence studies in August-September 2020 showed that there are 26-32 actual cases for every reported case in the country. If we set the Cynic-o-Meter to 32x, we have had around 320 million cases, corresponding to 25 per cent of the population of the country. In an earlier study, ICMR had proposed a correction factor of 80-100 per reported case, which permits us to dial up the Cynic-o-Meter all the way to 100x, to a billion cases, close to 75 per cent of the population.
Could this be right? Given that new cases are declining across the country, and the herd immunity threshold is estimated to be around 67 per cent, it is possible that close to a billion Indians have antibodies for Covid-19. Possible yes, but not likely.
That’s because the India-wide figures are misleading. As I wrote in an earlier column, we have had hundreds of local epidemics across the country; with densely populated and urban areas being more affected than others. Lockdowns, post-lockdown control measures, and public compliance were more effective in some areas and less in others. What we can say is this: wherever new cases are declining, we know that around 67 per cent of the “exposed” population possibly has immunity to the virus. Exposed population is the fraction that did not isolate itself adequately, the people who were not strict about masks, handwashing, and social distancing. It follows that if the exposed population in any city or district was large and new cases are few and declining, then the chances of a second wave are small. Cynicism will suggest that this indeed has been the case in India, where it is not uncommon to see the nose poking out of the mask, if at all there is a mask on the face.
This, then, is the basis for optimism. The risk of a second wave is small in most places across the country because most people have already been exposed. For the same reason, we might not need to be overly concerned about the new variants either.