Looking ahead: Karen Weise, a Times reporter who has been covering the virus from Washington State, said school closures could worsen the strains on nurses: “It’s hard to work, you end up with nurses who stay home with their kids, and then you might have a short-staffed medical facility.”

How worried should we be?

It’s the question on everyone’s minds, but a difficult one to answer, writes Max Fisher, one of our Interpreter columnists.

First, there’s still a lot we don’t know about the coronavirus. Because many cases are mild and some are asymptomatic, it’s difficult to track its deadliness and the extent of its spread.

Second, the risk level largely depends on how prepared societies are to deal with the virus. This is thought to be a reason that the death rate in China, where the virus first emerged late last year, is around 4 times that of South Korea, which was able to prepare before the virus arrived.

In December, Mr. Fisher got pneumonia — an illness similar to the one caused by the virus — and that experience helped clarify how an outbreak could affect society as a whole. While he was sick, family and friends helped with personal obligations, and he was able to quickly see doctors and get prescriptions.

“If a big fraction of my neighborhood in West London had all fallen sick at once, it would’ve been a different story,” he said. His local health office might not have been able to see him as quickly. Friends and family could have other sick people to help, or could be sick themselves.

“The risk from the virus’s impact on you individually is probably low,” he concluded. But its impact on society could be profound.