By Emily Schmall and Hari Kumar

NEW DELHI — India’s coronavirus crisis, which was killing thousands of people a day just seven months ago, has eased after the nation’s leaders revamped their policies and dramatically ramped up their vaccination drive.

Now, as India celebrates the delivery of its 1 billionth dose, a feat that until recently seemed improbable, public health experts are sounding a new warning: The turnaround is losing steam.

Vaccinations are slowing down. As the temperature dips amid India’s most important festival season, people are crowding markets and hosting unmasked friends and family indoors. And the government is telling vaccination campaign volunteers like Namanjaya Khobragade that they are no longer needed.

“Now is not the time to let our guard down,” said Khobragade, a coordinator for a health nonprofit in the eastern state of Jharkhand. “Many people have taken just the first vaccine. We cannot leave them like this. We need to increase the intensity.”

India’s progress represents a significant step toward ending the crisis globally and stands as an important political win for Prime Minister Narendra Modi, whose government came under heavy criticism for failing to prepare for a devastating second wave that struck earlier this year. After the virus killed tens of thousands of people, India’s government threw money at boosting vaccine production, stopped vaccine exports and tossed out cumbersome rules that had made it hard for state governments to get doses and for people to sign up for shots.

By official figures, daily infections have plunged to about 12,000 per day, from about 42,000 four months ago. Deaths, too, have fallen by half, to about 400 per day.

Experts consider India’s statistics on infections and deaths to be a gross undercount. Still, normal life has returned in many parts of the country. Shopping malls are crowded, roads are full of traffic, and children who have been out of school since March 2020 finally returned to classrooms this month.

But with only one-quarter of its vast population fully vaccinated, India remains deeply vulnerable. The possibility that a dangerous variant will emerge remains a concern.

The central government appears to acknowledge that India has lost a step. Shortly after returning from the climate conference in Scotland, Modi led a meeting focused on parts of the country where fewer than half the residents are fully vaccinated.

“Now we are preparing to take the vaccination campaign to each household,” he said in a statement, adding that officials would take a “knock on every door” approach toward “every household lacking the security net of a double dose of vaccine.”

Complacency contributed to the devastation of the second wave. In January, with India reporting case numbers comparable to this fall’s, Modi declared victory over the coronavirus. The government, encouraged by a flawed mathematical model that showed the pandemic had all but ended in India, prioritized vaccines for health care workers and older people with conditions that made them more likely to die from COVID-19.

For everybody else, the government moved more slowly. The Serum Institute of India, the world’s largest vaccine-maker, set aside 100 million doses of the AstraZeneca-Oxford University vaccine for its home country in January. That month, Modi’s government bought just 11 million doses. It exported more than five times that number as far afield as the Caribbean.

“There was an unfortunate sense of overconfidence that the pandemic had ended with India,” said Dr. K. Srinath Reddy, president of the Public Health Foundation of India.

Then the second wave hit. At its peak in May, India was reporting more than 400,000 new cases each day. Demand for vaccines skyrocketed. To cope, Modi’s government introduced a vaccine pricing system intended to direct doses to those with the greatest need. Instead, cities fought over limited supplies and corporations stockpiled, worsening the shortages.

By June, five months into the national vaccination campaign, just over 3% of the population had been inoculated.

As criticism from opposition parties grew, Modi centralized the procurement and distribution of vaccines. India’s inoculation program hit its stride, making use of the systems and know-how that had made vaccine campaigns against polio and other diseases such a success.

He shelled out billions of dollars — the government has not disclosed the precise amount — from India’s budget for an advance payment deal that allowed the Serum Institute to ramp up production to 220 million doses per month. It struck a similar deal with another Indian vaccine-maker, Bharat Biotech.

With supplies shored up, Modi’s government enlisted an army of volunteers, including paramilitary forces, teachers and religious leaders, to help get shots into arms.

The Serum Institute now says the government has cumulatively purchased 1 billion doses. More than 3 out of 4 adults have received at least one shot. Modi’s government is now so confident that it will fully vaccinate all adults, some 900 million people, by the end of the year that it has lifted its eight-month ban on vaccine exports.

At a meeting of the world’s largest economies in Rome last month, Modi said India would be able to supply 5 billion doses toward the global vaccination effort next year.

That may be good news for the world, but at home, health experts warn that the government needs to stay vigilant. Health workers are struggling to persuade millions of people to return for a second dose.

The vaccination rate has fallen sharply from its peak on Modi’s birthday in September, when 25 million doses were administered, and now totals about 3 million per day. India still has to administer more than 700 million shots to reach its year-end goal, which at current rates looks increasingly unlikely unless India can repeat Modi’s birthday feat a few more times.

“There is hesitancy for going for the second dose because the community thinks, ‘Do we really need it now?’” said Dr. Jacob John, a public health physician in the southern Indian state of Tamil Nadu. The makeshift groups the government tapped to drive the vaccine push, he added, were not built for a sustained campaign.

Delays could open opportunities for a new variant to strike or for immunity to ebb. Recent serological prevalence surveys, which measure antibodies that form in response to infection or a vaccine, show that some of India’s largest cities, including the capital of New Delhi, are reporting upward of 90% with antibodies.

“But it’s not a uniform distribution across the country,” Reddy said. “You have pockets of vulnerability.”

The Indian government seems to know that it has a long way to go. India recently applied for a $2 billion loan with the Asian Development Bank and Asian Infrastructure and Investment Bank to buy doses for some 300 million more people.

Administering a billion doses “is an important milestone,” N.K. Arora, the head of India’s National Expert Group on Vaccine Administration, wrote in a newspaper op-ed, “but the fact is that there is still a long road to effectively control COVID.”

In Jharkhand, Khobragade, the health worker, said myths remain rampant among some villagers that the vaccine is deadlier than the coronavirus, makes men impotent or — among Muslim and Christian worriers — converts people to Hinduism.

Khobragade plunged into the vaccine campaign in April, when entire villages were coming down with COVID, and the constant smoke from funeral pyres blackened the skies of New Delhi.

Now, with a major milestone reached, the state government is saying Khobragade can return to her work on maternal and infant health. It has withdrawn funding and the extra vaccine vans and nursing staff Khobragade relied upon to reach hesitant villagers.

“There is still huge vaccine hesitancy,” she said. “Now is no time to rest.”

-New York Times