NEW YORK (AP) — What is this enemy?

Seven months after the first patients were hospitalized in China battling an infection doctors had never seen before, the world has reached an unsettling crossroads.

Countless hours of treatment and research, trial and error now make it possible to take much closer measure of the new coronavirus. But to take advantage of that intelligence, we must confront our persistent vulnerability.

"It's like we're in a battle with something that we can't see, that we don't know, and we don't know where it's coming from," said Vivian Castro, a nurse supervisor at St. Jos...