NEW DELHI: One in every four Indians possibly has antibodies to fight the novel coronavirus, according to Covid-19 tests done by a national-level private laboratory.
Surveys done at the city level by various civic corporations and some of the country’s best research organisations (TIFR, IISER) are more encouraging. Pune on Monday reported over 50% sero-positivity in certain pockets, Mumbai reported 57% positivity in slum areas. Delhi’s first survey showed 23% of those tested were sero-positive. The results of a second survey are expected this week.
When an individual has antibodies, he/she has immunity to Covid-19, though the jury is still out on whether this is short- or long-term immunity. When many in the community have antibodies, it could lead to herd immunity against the novel coronavirus.
India is still far away from herd immunity as 60-70% of the population should ideally have antibodies (or exposure to the virus) to achieve it. But some experts believe Indian localities, suburbs or cities could be closer to herd immunity than many of their global counterparts. For example, 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.
“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.
The countrywide antibody tests carried out by Thyrocare laboratory show high levels of positivity at local levels. Managing director Arokiaswamy Velumani said almost 24% of the two-lakh plus people tested across the country so far have antibodies to Covid-19. Around 29% of Delhi’s tested population and 20% in Maharashtra are sero-positive, he added.
If 27% of Mumbai’s tested population showed exposure to the virus, it was every third person in neighbouring Thane city; the corresponding number for Navi Mumbai was 21%.
Within Mumbai, Thyrocare data shows higher levels of exposure: Vile Parle (E) showed the highest sero-positivity at 42.97%, followed by Worli at 41.94% and Dongri (39.41%).
“Our results show India at 24% positivity is getting closer to 35% when plateauing of cases is known to happen,” said Dr Velumani. At 45% of sero-positivity, the curve takes a downward slope. “With positivity anywhere between 45%-50%, the virus becomes less impactful,” he added.
According to Bangalore-based epidemiologist Dr Giridhara Babu, cities such as Delhi and Mumbai will achieve herd immunity first, with the Tier 2 and 3 cities that are witnessing the Covid-19 outbreak now catching up later.
“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.
So what has contributed to India’s supposedly ‘better’ fight against the coronavirus? Many believe it is the fact that India is a young country. “The average age of Indians is 29 years while it is 45 years in the US,” said Dr Babu. He added there is a need to study the “immuno dark matter” or the T cells that could be contributing to the raised immunity among Indians.
A doctor from a public hospital in central Mumbai said 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.
Mumbai-based endocrinologist Dr Joshi said immune response said a lot about the Covid curve in India. “The Indian trend shows we have had a largely asymptomatic disease. We have better recovery rates and lower fatality rates as compared to the West,” he said. Except for the elderly and those with co-morbidity, the overall picture looks good,” added Dr Joshi.
Courtesy Times of India