If you assume that herd protection could be achieved when 60 percent of the population becomes resistant to the virus, that means New York City is only one-third of the way there. And, so far, nearly 250 of every 100,000 city residents has died. New York City still has millions of residents vulnerable to catching and spreading this disease, and tens of thousands more who are at risk of dying.

“Would someone advise that people go through something like what New York went through?” said Natalie Dean, an assistant professor of biostatistics at the University of Florida. “There’s a lot of people who talk about this managed infection of young people, but it just feels like hubris to think you can manage this virus. It’s very hard to manage.”

In other cities, serology surveys are showing even smaller shares of people with antibodies. The quality of these studies is somewhat varied, either because the samples weren’t random or because the tests were not accurate enough. But the range of studies shows that most places would have to see 10 or more times as many illnesses – and possibly, deaths – to reach the point where an outbreak would not be able to take off.