Is India closer to herd immunity against Covid-19?

Almost 24 per cent of the 200,000 plus people tested across India so far have antibodies to Covid-19.

According to some experts Indian localities, suburbs or cities could be closer to herd immunity after surveys showed that one in every four Indians possibly has antibodies to fight the Covid-19.

Herd immunity occurs when many in the community have antibodies against the virus, however it is not yet ascertained whether this is short or long-term immunity.  

While India is still far away from herd immunity as 60 to 70 per cent of the population should ideally have antibodies (or exposure to the virus) to achieve it, surveys done at the city level by various civic corporations and research organisations (TIFR, IISER) are more encouraging.

Pune on Monday reported over 50 per cent sero-positivity in certain pockets, Mumbai reported 57 per cent positivity in slum areas and Delhi's first survey showed 23 per cent of those tested were sero-positive.

"India is the only country with areas showing such high sero-positivity. Clearly, Indians are immunologically stronger," said Maharashtra Covid task force member Dr Shashank Joshi. Dharavi in Mumbai has been recording near-zero (single-digit) transmission for the last two months after being the country's worst hotspot in April-May, according to a report in Times of India.

The countrywide antibody tests were carried out by Thyrocare laboratory and showed high levels of positivity at local levels. Its managing director, Arokiaswamy Velumani, said almost 24 per cent of the 200,000 plus people tested across India so far have antibodies to Covid-19. The results of a second survey are expected this week.

"Our results show India at 24 per cent positivity is getting closer to 35 per cent when plateauing of cases is known to happen. With positivity anywhere between 45 and 50 per cent the virus becomes less impactful," said Velumani, adding that at 45 per cent of sero-positivity the curve takes a downward slope.

According to Bangalore-based epidemiologist Dr Giridhara Babu, cities such as Delhi and Mumbai will achieve herd immunity first. "We have 39 deaths per million population across India. In metros such as Delhi and Mumbai, this figure goes up to 200. But the West has recorded almost 600 deaths per million population," said Dr Babu.

He pointed out that there is a need to study the "immuno dark matter" or the T cells that could be contributing to the raised immunity among Indians. "The average age of Indians is 29 years while it is 45 years in the US," said Dr Babu, stressing that many believe it is the fact that India is a young country.

While a doctor from a public hospital in central Mumbai believes that the hygiene hypothesis may hold the answer. "We Indians have been exposed to so many microorganisms that we have a better immune response," he said.

• India