NEW DELHI – When the coronavirus pandemic hit India, there were fears that it would sink the fragile health care system of the second most populous country in the world. Infections increased dramatically for months and at one point India looked like it could overtake the United States as the country with the highest number of cases.
But infections started to plummet in September, and the country is now reporting about 11,000 new cases a day, compared to a peak of almost 100,000, leaving experts perplexed.
They suggested many possible explanations for the sudden drop – seen in almost all regions – including that some areas of the country may have achieved herd immunity or that the Indians may have some pre-existing protection against the virus.
The Indian government has also partially attributed the drop in cases to the use of a mask, which is mandatory in public in India and the violations result in heavy fines in some cities. But experts noted that the situation is more complicated, as the decline is uniform, although mask compliance is declining in some areas.
It is more than just an intriguing puzzle; determining what is behind the drop in infections can help authorities control the virus in the country, which has reported nearly 11 million cases and more than 155,000 deaths. About 2.4 million people died worldwide.
“If we don’t know why, you may be unconsciously doing things that could lead to an outbreak,” said Dr. Shahid Jameel, who studies viruses at Ashoka University in India.
India, like other countries, loses many infections and there are doubts about how it is counting virus deaths. But pressure on hospitals across the country has also eased in recent weeks, yet another indication that the spread of the virus is slowing. When registered cases exceeded 9 million in November, official figures showed that almost 90% of all intensive care beds with ventilators in New Delhi were full. As of Thursday, 16% of these beds were occupied.
This success cannot be attributed to vaccinations, as India only started administering the vaccines in January – but as more people get vaccinated, the outlook should look even better, although experts are also concerned about the variants identified in many countries that appear to be more contagious and make some treatments and vaccines less effective.
Among the possible explanations for the drop in cases is the fact that some large areas have reached herd immunity – a limit in which a sufficient number of people have developed immunity to the virus, when they get sick or are vaccinated, that the spread begins to decrease, he said Vineeta Bal, who studies the immune system at India’s National Institute of Immunology.
But experts warned that even though collective immunity in some places is partly 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 that people who have become ill with a form of the virus can be infected again with a new version. Bal, for example, pointed to a recent survey in Manaus, Brazil, which estimated that more than 75% of people there had antibodies to the virus in October – before cases increased again in January.
“I don’t think anyone has the final answer,” she said.
And in India, the data is not so dramatic. A national screening of antibodies by Indian health agencies estimated that about 270 million, or one in five Indians, had been infected by the virus before vaccination started – which is well below the rate of 70% or more than experts are said to be the limit for coronavirus, although even that is not certain.
“The message is that a large proportion of the population remains vulnerable,” said Dr. Balram Bhargava, who heads India’s main medical research body, the Indian Medical Research Council.
But the research offered other information about why infections in India may be decreasing. He showed that more people were infected in India’s cities than in their villages, and that the virus was spreading more slowly in the rural interior.
“Rural areas are less densely populated, people work more in open spaces and houses are much more ventilated,” said Dr. K. Srinath Reddy, president of the Public Health Foundation of India.
If some urban areas are approaching herd immunity – whatever that limit is – and are also limiting transmission through masks and physical distance and are therefore seeing falling cases, then perhaps the low speed with which the virus going through rural India can help explain falling numbers, suggested Reddy.
Another possibility is that many Indians are exposed to a variety of diseases throughout their lives – cholera, typhoid and tuberculosis, for example, are prevalent – and this exposure can prepare the body to mount a stronger initial immune response to a new virus. .
“If the COVID virus can be controlled in the nose and throat, before it reaches the lungs, it does not become so severe. Innate immunity acts at this level, trying to reduce viral infection and prevent it from reaching the lungs, ”said Jameel, from Ashoka University.
Despite the good news in India, the emergence of new variants has added another challenge to efforts here and around the world to control the pandemic. Scientists have identified several variants 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 implications for public health.
Experts are considering whether the variants may be driving an increase in cases in the southern state of Kerala, which had previously been hailed as a model for fighting the virus. Kerala now accounts for almost half of the current cases of COVID-19 in India. Government-funded research has suggested that a more contagious version of the virus could be at stake, and efforts to sequence its genome are underway.
As the reasons behind India’s success are unclear, experts fear that people will let their guard down. Much of India has now returned to normal life. In many cities, markets are crowded, roads are crowded and restaurants are almost crowded.
“With the reduction in numbers, I feel that the worst of COVID is over,” said MB Ravikumar, an architect who was hospitalized last year and recovered. “And we can all breathe a sigh of relief.”
Perhaps not yet, said Jishnu Das, a health economist at Georgetown University who advises the state of West Bengal on how to deal with the pandemic.
“We don’t know if this will return after three to four months,” he warned.
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