Herd immunity in India may generate only in pockets, can be short-lived: Scientists

New Delhi: Herd immunity against Covid-19 in India is likely to be achieved only in pockets given the many socio-economic groups in the country and maybe short-lived rather than long-lasting, say scientists as sero-surveillance data from New Delhi and Mumbai raise hopes of ‘community protection’ from the disease.

Herd immunity occurs when a large number of people, usually 70 to 90 per cent, become immune to a contagious disease after being infected to it.

But there are many grey areas clouding the issue as far as the novel coronavirus is concerned with no consensus on when herding immunity sets in.

“There are no clear numbers to say at what per cent of the infected population we will achieve herd immunity. Many epidemiologists believe that for SARS-CoV-2 it would be at around 60 per cent,” said Shahid Jameel, virologist and CEO of the Wellcome Trust/DBT India Alliance, a public charity that invests in building biomedical sciences and health research frameworks.

He said different parts of the country will get closer to herd immunity at different times.

A recent study published in the journal Science also found that herd immunity against Covid-19 could be achieved with fewer people being infected than previously estimated.

“Herd immunity is determined primarily by how many individuals in a population are immune to a particular infection. This results in indirect immunity to others in the population who never got exposed or infected,” explained virologist Upasana Ray.

“Essentially, herd immunity means that the more the number of people get infected and develop immunity, the less chance there is for others in the population to get infected,” Ray, senior scientist at CSIR-IICB, Kolkata, told PTI.

Immunologist Satyajit Rath agreed that it was not known at what point of the infection herd immunity would set in.

“In India, with its multitude of socio-economic groupings, herd immunity may be generated in pockets rather than uniformly across the country, and maybe short-lived,”Rath, from New Delhi’s National Institute of Immunology, told PTI.

“And therefore, the idea of naturally generated long-lasting herd immunity may not be of much practical policy relevance for India,” he added.

The debate on herd immunity intensified following sero-surveys from New Delhi and Mumbai, two of India’s most populated cities where the number of Covid-19 cases surged before showing a declining trend.

The sero-surveillance study in Mumbai revealed that 57 per cent of its slum population and 16 per cent of its non-slum residents in three civic wards had developed antibodies, indicating many people would already be affected by Covid-19 than the official tally suggests.