India is nowhere close to achieving "herd immunity" against Covid-19 despite a few pockets in Delhi, Mumbai and Pune reporting 50-60% of people’s exposure to the novel coronavirus, necessitating continuation of the vaccination programme.
Sources in the Indian Council of Medical Research told DH that its third nation-wide sero-survey found less than 25% of India’s population was exposed to the SARS-CoV-2. The agency is yet to make the survey results public.
During the early stages of the Covid-19 pandemic, medical researchers had predicted that herd immunity for Covid-19 is likely to occur when nearly 70% of the population is infected.
Two previous rounds of nationwide sero-surveys conducted by ICMR found that Covid-19 infection prevalence had increased from 0.7% in May to 7% in August last year.
The third sero-survey, results of which may be released within days, found that the exposure level increased to more than 20%.
"This means, there are still 80% people who are vulnerable and we are nowhere close to herd immunity," said an ICMR scientist.
The fifth round of Delhi sero-survey has reportedly found antibodies in more than 50% of the national capital’s population and at least in one of the districts, nearly 58% of the population was exposed to the virus.
Around 25,000 people were sampled for the survey, which ended a week ago and the results are yet to be officially released.
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In November, a similar survey conducted in five wards of Pune on a sample size 1,659 people detected the presence of antibodies in 85% of the population. In Mumbai, nearly 57% of the slum population have antibodies.
The hopes of reaching herd immunity, however, ended there. Most of the states including Kerala – the current epicentre of the epidemic – did not carry out any sero-survey and of those who did the first round, very few are attempting a second round.
Kerala is yet to conduct an extensive sero-surveillance. Though the government announced on January 3 that an extensive one would be carried out, it is yet to begin. "The West Bengal government has not conducted any sero-survey to gauge the spread of Covid-19 in Bengal," said Ajay Chakraborty, Director of Health Services in Bengal.
The first round in Karnataka showed 27% of the people were infected and a second round is going on. Andhra Pradesh did a sero-survey in November but its results have not yet been released. The second round of sero-prevalence in Kashmir conducted in November showed 38.8% of the population had developed antibodies. It was 16% in the non-slum settings in Mumbai, 7.8% in Indore, 22.7% in Puducherry, and 32.3% in Chennai.
"It took nearly 20 years to develop near total immunity against polio in India. In Mumbai – which was the Covid-19 epicentre till a few months ago, there could be herd immunity in localised areas like Dharavi or Worli but not the entire city and its suburbs," said Avinash Bhondwe, president of the Maharashtra chapter of Indian Medical Association.
(With inputs from Suraksha P, Soumya Das, Arjun Raghunath, Zulfikar Majid, Mrityunjay Bose and Prasad Nichenametla)
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