23% of Delhiites Exposed to Coronavirus. Are We Inching Closer to Herd Immunity?


23% of Delhiites Exposed to Coronavirus. Are We Inching Closer to Herd Immunity?

Illustration: Reynold Mascarenhas

A recently completed study in Delhi found that a much larger portion of the population has been exposed to the coronavirus than the number of positive cases in the city indicate. Could this be an indication that the population might be evolving herd immunity? Results from a serological survey conducted in Delhi found that 23.48 per cent of the population had traces of Immunoglobulin G (IgG) antibodies in their blood.

IgG antibodies are among the most common antibodies found in the human body, and their presence in a person’s bloodstream is an indication that they have been recently exposed to the coronavirus. Conducted on a sample grouping of 21,387 subjects chosen at random, the serological survey found that far more people had been exposed to the coronavirus than the ones testing positive. Some experts pointed out that this may be a sign of an evolving herd immunity, which is achieved when enough members of a population have been exposed to a virus and had their bodies develop a natural immune response to it.

A recent drop in the number of deaths and positive cases in Delhi seems to hint toward herd immunity playing a possible role. In a similar example, eminent epidemiologist Jayaprakash Muliyil pointed to a sharp fall in the number of new cases and deaths in Mumbai’s Dharavi, a densely pocketed area. Muliyil stated that the sudden flattening of the curve in Dharavi could be credited to the local population being exposed to the virus and developing antibodies to fight it in the process.

However, not all experts agree that herd immunity is close to being achieved. And even if it is, there are doubts over its longevity and efficiency. Nirmal Kumar Ganguly, the former Director-General of the Indian Council for Medical Research (ICMR), said in an interview that the natural antibodies produced by the body are not long-lived, after which the individual can become susceptible to the disease again.

This is probably why, despite the hints of herd immunity seen in Delhi’s serological survey, the Ministry of Health and Family Welfare put out a statement saying “Containment measures need to continue with the same rigour.”