The slowdown reflects the social distancing that has been happening in these places over the past two weeks. Yet even if the slowdown persists, it is far, far too early to be optimistic about the virus’s trajectory.

For one thing, serious symptoms trail new infections by several days or more. The number of deaths in New York and nationwide is likely to spike over the next week. At a single hospital in Queens yesterday, 13 people died — a scene that Ashley Bray, a doctor there, described as “apocalyptic.” The coming spike in hospitalizations could easily overwhelm hospitals, especially because of the shortage of medical equipment.

For another, not every part of the country has engaged in rigorous social distancing. Cases in Republican-leaning states, especially in the South, are now growing more quickly than in Democratic-leaning states, as Nate Silver noted yesterday. One likely reason is that many Republicans, taking their cues from President Trump and some other party leaders, still don’t view the virus as a threat, as polls show. My colleague Jennifer Senior argues that other states are different from New York more in timing than degree: “The idea that New York is an exception rather than a harbinger is madness,” she writes.

Whatever happens over the next week or two, the country still has no viable way to start functioning normally again without a huge increase in testing. Even if new cases slow, the return of typical activity will cause new outbreaks. “Testing will allow us to isolate the infected so they can’t infect others,” Aaron Carroll and Ashish Jha, both medical school professors, wrote in The Atlantic.

Or as Tedros Adhanom Ghebreyesus, director general of the World Health Organization, said yesterday: “Asking people to stay at home and shutting down population movement is buying time and reducing the pressure on health systems. But on their own, these measures will not extinguish epidemics.”