“We may be at a turning point,” Marcus Plescia, chief medical officer at the Association of State and Territorial Health Officials, said of the pandemic. “We have a lot more tools now to fight it.”

Public-health experts say factors driving the decline likely include an incremental uptake in vaccines, the return of precautions like mask-wearing in certain areas and growing immunity in the population due to Delta’s rapid spread in hard-hit states including Mississippi and Florida…

There are reasons for caution, health authorities say. The U.S. posted its worst numbers of the pandemic, including a quarter-million new cases a day, shortly after the winter holidays last year, when colder weather and family gatherings brought more people together indoors where the virus most easily spreads.

In the U.K., where the vaccination rate is higher than in the U.S., cases remain high after the country bet on immunity from vaccines and prior infections while dropping other measures like indoor crowd limits and mandatory mask-wearing.