India’s steep fall in virus lifts hopes

Health experts left guessing at reason for infection slump

By Krutika Pathi and Aniruddha Ghosal

NEW DELHI — When the coronavirus pandemic took hold in India, there were fears it would sink the fragile health system of the world’s second-most populous country. Infections climbed dramatically for months and at one point India looked like it might overtake the United States as the country with the highest case toll.

But infections began to plummet in September, and now the country is reporting about 11,000 new cases a day, compared to a peak of nearly 100,000, leaving experts perplexed.

They have suggested many possible explanations for the sudden drop — seen in almost every region — including that some areas of the country may have reached herd immunity or that Indians may have some preexisting protection from the virus.

The Indian government has also partly attributed the dip in cases to mask-wearing, which is mandatory in public in India. But experts have noted the decline is uniform even though mask compliance is flagging in some areas.

It’s more than an intriguing puzzle; determining what’s behind the drop could help authorities control the virus in the country, which has reported nearly 11 million cases and over 155,000 deaths. More than 2.4 million people have died worldwide.

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

India, like other countries, misses many infections, and there are questions about how it’s counting virus deaths.

But the strain on the country’s hospitals has also declined in recent weeks, a further indication the virus’s spread is slowing. When recorded cases crossed 9 million in November, nearly 90% of all critical care beds with ventilators in New Delhi were reported full. Last Thursday, 16% of these beds were occupied.

That success can’t be attributed to vaccinations since India only began administering shots in January.

Among the possible explanations for the fall in cases is that some large areas have reached herd immunity — the threshold at which enough people have developed immunity to the virus, by falling sick or being vaccinated, so that the spread begins to slacken, said Vineeta Bal, who studies immune systems at India’s National Institute of Immunology.

But experts h ave cautioned that even if herd immunity in some places is partially responsible for the decline, the population as a whole remains vulnerable — and must continue to take precautions.

This is especially true because new research suggests people who got sick with one form of the virus may be able to get infected again with a new version.

Bal, for instance, pointed to a recent survey in Manaus, Brazil, that estimated that over 75% of people there had antibodies for the virus in October — before cases surged again in January.

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

But the survey offered other insight into why India’s infections might be falling. It showed that more people had been infected in India’s cities than in its villages, and that the virus was moving more slowly through the rural hinterland.

“Rural areas have lesser crowd density, people work in open spaces more and homes are much more ventilated,” said Dr. K. Srinath Reddy, president of the Public Health Foundation of India.

Another possibility is that many Indians are exposed to a variety of diseases throughout their lives — cholera, typhoid and tuberculosis, for instance, are prevalent — and this exposure can prime the body to mount a stronger, initial immune response to a new virus.

Despite the good news, scientists have identified several variants of the virus in India, including some that have been blamed for causing new infections in people who already had an earlier version of the virus. But they are still studying the public health implications.

Experts are considering if variants may be driving a surge in cases in the the southern state of Kerala, which had previously been hailed as a blueprint for tackling the virus.

Kerala now accounts for nearly half of India’s current

COVID-19 cases. Government-funded research has suggested that a more contagious version of the virus could be at play.

With the reasons behind India’s success unclear, experts are concerned that people will let down their guard. In many cities, markets are heaving, roads are crowded and restaurants nearly full.

“I feel that the worst of COVID is over,” said M. B. Ravikumar, an architect who was hospitalized last year and recovered. “And we can all breathe a sigh of relief.”

Maybe not yet, said Jishnu Das, a health economist at Georgetown University who advises the West Bengal state on handling the pandemic.

“We don’t know if this will come back after three to four months,” he warned.

MANISH SWARUP/AP People wait outside a health center to get tested for COVID-19 last week in New Delhi.