NEW DELHI — Back in November, Ajeet Jain felt like he was living a nightmare. The large public hospital where he works in India's capital was full of covid-19 patients, hundreds of them so ill they required intensive care. About 10 people were dying every day.
The apparent retreat of the coronavirus in India, the world’s second-most populous nation, is a mystery that is crucial to the future course of the pandemic.
Just months ago, India was adding nearly 100,000 cases a day — more than any other country. On Tuesday, it reported only 8,635. That’s about the number recorded the same day by New York state, where the population is less than 2 percent of India’s.
Epidemiologists in India say that there is only one likely explanation for the decrease in new cases: The virus is finding it harder to spread because a significant proportion of the population, at least in cities, already has been infected.
The decline is not related to a lack of opportunities for transmission. India has fully reopened its economy, with elementary schools being the only major exception. Restaurants, malls and markets are bustling. Masks are common in some indoor settings and mandatory in Delhi and Mumbai, but in many parts of the country, they’re scarcely seen on the streets.
India has reported 10.8 million coronavirus cases in total, although that is likely to be a vast undercount. The results of a nationwide antibody survey of 28,600 people by the government released on Thursday indicated that more than 1 in 5 Indians — about 270 million people — had been exposed to the virus as of early January.
In major cities, infection rates are even higher. On Tuesday, Satyendar Jain, the health minister for Delhi, announced that a recent study of 28,000 people in India’s capital found 56 percent had coronavirus antibodies. Earlier antibody surveys of certain neighborhoods in Mumbai and Pune also found that a large proportion of the residents had been infected.
By comparison, a study published last month estimated that more than 14 percent of the population in the United States had coronavirus antibodies as of mid-November.
Such antibody surveys have proved sensitive for health officials in India. They indicate that the actual number of infections in the country is far higher than the official tally and that efforts to contain the spread of the virus in cities largely failed. The surveys also show that most cases of coronavirus infection went undetected despite a significant increase in testing.
The number of daily tests in India has decreased somewhat in recent weeks, but the drop in case numbers predated that decline. The rate of positive tests also has tumbled from 9 percent in September to below 2 percent.
India’s big cities probably have “reached the threshold of population immunity,” said Giridhar Babu, an epidemiologist at the Public Health Foundation of India. The virus will continue to spread, he added, but “the quantum of infected cases will not be the same.”
Epidemiologists are quick to add notes of caution. How new variants of the virus will affect infections in India is unclear, and vaccination remains critical to warding off a possible second wave. The variant first detected in Britain is already in circulation here, and experts say India needs to expand its genetic surveillance of cases to understand how mutations are spreading.
“When you start seeing the new strains, you may see problems,” said Jacob John, an epidemiologist and community health physician in the state of Tamil Nadu. But “with a combination of natural infections and now vaccines, we might be able to beat this.”
If the novel coronavirus has infected a large portion of India’s urban population, as epidemiologists believe, much remains to be explained about the country’s rate of covid-19 deaths. India has recorded 155,000 deaths, or about 112 per 1 million of population, compared with 1,362 per million in the United States.
Some of that difference is attributable to covid-19 deaths missing from India’s official figures. But experts think that other factors have helped to reduce India’s death rate, including its predominantly young population. Other researchers speculate that some still-unknown immunological factor is making infections less severe.
“Our mortality is relatively low in India and that, in the end, is saving the day,” said Aurnab Ghose, a biologist at the Indian Institute of Science Education and Research. Understanding why will require much more research, he said, and the answers probably will not emerge for “years to come.”
Ghose was part of a research team that conducted an antibody survey in several districts of Pune, a city in western India that had one of the worst outbreaks of novel coronavirus infections in the country. Then they watched to see the pattern of new cases in those districts over the next four months.
The result was a “remarkable correlation,” Ghose said. The districts with the highest presence of antibodies among the population had the fewest new infections. He thinks that urban India is unlikely to see a second wave like the one in Europe, as long as existing antibodies offer some protection against new variants of the virus.
The falling case numbers risk undermining India’s ambitious push to vaccinate 300 million people by summer. With the virus in retreat, some people may feel less urgency to be immunized amid worries about possible side effects. That’s a mistake, said Bhramar Mukherjee, a biostatistician at the University of Michigan who developed a model to track India’s outbreak.
“You really don’t know the future,” she said. “You don’t know how long disease-induced immunity lasts.”
Since launching its vaccination drive on Jan. 16, India has given doses to more than 4 million people. The government says it reached that milestone faster than the United States, Britain or Israel. But it must accelerate the pace significantly if it is to meet its own target.
Among the medical personnel on the front lines of the pandemic in India, there is amazement that the threat they faced has receded. In September, Vidyadhar Gaikwad was scrambling to secure oxygen supplies for his large public hospital in Pune as the number of coronavirus cases soared. At one point, the hospital had nearly 400 covid-19 patients; now it has 12.
The cases have “gone down remarkably,” Gaikwad said.
For Jain, the doctor in Delhi, the change can be measured in other ways, too. Not so long ago, people were afraid even to set foot in Rajiv Gandhi Super Specialty Hospital, the place where he works. Now they’re coming in and “sitting and talking to each other,” he said.
Jain worries about a possible resurgence of cases such as the one Europe experienced. But he also allows himself a measure of hope. “I’m a bit optimistic that this disease is over,” he said.
Taniya Dutta contributed to this report.