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Saturday, August 15, 2020

Parts of India may have achieved herd immunity to COVID-19

Coronavirus: some India slums ‘may have reached herd immunity’, study finds | South China Morning Post - Bloomberg:

July 30, 2020 - "'Mumbai’s slums may have reached herd immunity,' said Jayaprakash Muliyil, chairman of the Scientific Advisory Committee of India’s National Institute of Epidemiology, and the retired head of one of its premier medical colleges. 'If people in Mumbai want a safe place to avoid infection, they should probably go there.'

"The findings of the study, which was conducted by municipal authorities and the Tata Institute of Fundamental Research, suggest that despite efforts to contain its spread, Mumbai’s poorest places may have unwittingly pursued the controversial strategy of herd immunity.... About 57 per cent of surveyed people in the slums of Dahisar, Chembur and Matunga had antibodies in their blood, compared to 21.2 per cent found in an April study in New York City, and 14 per cent reported in Stockholm in May.

"A 'hands-off' approach has been criticised in places like Sweden.... But the findings from Mumbai’s slums, where the population is young and less predisposed to severe cases of Covid-19, may support public health strategies more focused on protecting the vulnerable without trying to suppress the virus completely.

"With social-distancing generally impossible, Mumbai’s slums are singularly well-suited for the coronavirus’ spread. Dharavi, the largest, is home to some 1 million people and has a population density of 277,136 per square kilometre. As many as 80 people often share a public toilet, and families of eight regularly packed in a 100-square-foot room.

"Yet the slums have seen steep drops in infections in recent weeks after cases first erupted in April, even as India’s overall cases grow at the fastest pace globally. Credit has largely been given to the intensive containment measures officials implemented in the slums, like door-to-door health screenings and rapidly-erected quarantine facilities. The serological findings suggest another possibility: the crisis may be largely over because the virus has spread efficiently, not because it was stopped.

"Muliyil said.... 'The virus doesn’t worry about your quarantine and it is much more efficient than your efforts to contain it.'  He does, however, credit the government’s containment measures with keeping mortality rates low in the slums, because the proactive surveillance ensured that cases were caught early and given high quality care.... Dharavi has recorded 253 deaths.

"Growing herd immunity may also be behind the dip in cases in the capital city of New Delhi, said Muliyil, where a study in early July found that a quarter of the population had been exposed. Epidemiologists generally believe that infection levels must reach 60 per cent to create herd immunity. But exposure concentrated in the populations least able to socially distance could still slow the overall spread of infection.

"In Mumbai overall, new cases dropped to the lowest tally in almost three months this week, although the July antibody survey found only 16 per cent had been exposed to the virus among those living in places where social distancing is more feasible, like apartment buildings and houses."

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