Why India's very high COVID caseload continues to plummet

Exposure to previous major illnesses may contribute

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India’s coronavirus caseload is falling dramatically — and medical experts are stumped as to why. The number of COVID-19 cases rose by just over 9,000 Tuesday — down from a peak of nearly 100,000 a day leading into September.

Tough fines on those caught not wearing a mask may be one reason. Another is that some regions may have reached herd immunity, the Associated Press reports. Yet another is that some experts also suggest Indians may be able to mount a stronger, initial immune response because of exposure to cholera, typhoid or tuberculosis.

Determining what’s behind the drop in infections could help authorities control the virus in the country, which has reported nearly 11 million cases and more than 155,000 deaths. The U.S., with the world’s highest case count, has recorded 486,000 deaths.

“If we don’t know the reason, you could unknowingly be doing things that could lead to a flare-up,” Dr. Shahid Jameel, who studies viruses at India’s Ashoka University, told the AP.

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The number of occupied ICU beds with ventilators has fallen from 90 per cent in New Delhi in November to just 16 per cent last week. But given that vaccine programs in India were launched only in January, vaccinations have been ruled out as a possible explanation.

One intriguing possibility explaining the decline is that some large areas have developed herd immunity — the threshold at which enough people have developed immunity to the virus, by falling sick or being vaccinated, that the spread begins to slacken, Vineeta Bal of India’s National Institute of Immunology, told the AP. 

But India seems to be far from reaching herd immunity, with some 20 per cent of Indians having contracted COVID-19. That’s well below the 70 per cent minimum that experts believe could be the threshold.

Complicating a resolution is the emergence of new strains of the virus. Several have appeared in India, including some that have been blamed for causing new infections in people who already had an earlier version, a situation similar to the one in Manaus, Brazil. There, a recent survey estimated that more than 75 per cent of people had antibodies for the virus in October, but then the city experienced an even larger case count in January.

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Nearly half of India’s current cases are in the southern state of Kerala, which had been lauded as a model for tackling the virus. It is believed a more contagious version of the virus could be at play, and efforts to sequence its genome are ongoing.

“The message is that a large proportion of the population remains vulnerable,” Dr. Balram Bhargava, who heads India’s premier medical research body, the Indian Council of Medical Research, told the AP.

“If the COVID virus can be controlled in the nose and throat, before it reaches the lungs, it doesn’t become as serious. Innate immunity works at this level, by trying to reduce the viral infection and stop it from getting to the lungs,” said Jameel, of Ashoka University.

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