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 one 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 that they are no longer needed.

“Now is not the time to let our guard down,” said one of the volunteers, Namanjaya Khobragade, a coordinator for a health nonprofit in the eastern state of Jharkhand.

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.

While experts consider India’s statistics on infections and deaths to be a gross undercount, 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 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. “There is still huge vaccine hesitancy,” said Khobragade, the volunteer. “Now is no time to rest.”

Emily Schmall and Hari Kumar write for The New York Times.