The Pandemic Is Receding in the Worst Hotspots. Will It Last?

LONDON — A month ago, the pandemic looked bleak. More than 750,000 coronavirus cases were tallied worldwide in a single day. Infections surged across the entire United States. New variants identified in the United Kingdom, Brazil and South Africa threatened the rest of the world.

But the last month has brought a surprisingly fast, if partial, turnaround. New cases have declined to half their peak globally, driven largely by steady improvements in some of the same places that weathered devastating outbreaks this winter.

Cases are an imperfect measure, and uneven records and testing mask the scope of outbreaks, especially in parts of Africa, Latin America and South Asia. But fewer patients are showing up at hospitals in many countries with the highest rates of infection, giving experts confidence that the decline is real.

“It’s a great moment of optimism, but it’s also very fragile in a lot of ways,” said Wafaa El-Sadr, an epidemiologist at Columbia University’s Mailman School of Public Health. “We see the light at the end of the tunnel, but it’s still a long tunnel.”

The lull in many of the world’s worst outbreaks creates a critical opportunity to keep the virus in retreat as vaccinations begin to take effect. Experts believe vaccines have done little to slow most outbreaks so far, but a small group of countries, primarily wealthy ones, plan to vaccinate vulnerable groups by the spring.

The positive signs come with a number of caveats and risks.

Many countries are still struggling. Brazil is battling a serious resurgence in the face of a new variant discovered in the country. Hospitalizations in Spain are higher than they’ve ever been, even though official tallies show a decline in new cases. And in a number of European countries — the Czech Republic, Estonia and Slovakia — the infection rate is worsening.

More contagious variants — or just lapses in social distancing and other control measures — could still bring new spikes in infections that could outpace the positive effects of vaccination. A variant first found in Britain is spreading rapidly in the United States, and it has been implicated in surges in Ireland, Portugal and Jordan.

And while most countries have seen declines in cases over the past month, the total global reduction has been driven largely by just six countries with enormous epidemics.

There is no single cause behind the slowdowns, and the factors may differ in different places. Public health experts in the worst-hit countries attribute the progress to some combination of increased adherence to social distancing and mask wearing, the seasonality of the virus and a build-up o