In early January, when the first hazy reports of the new coronavirus outbreak were emerging from Wuhan, China, one American doctor had already been taking notes. Michael Callahan, an infectious disease expert, was working with Chinese colleagues on a longstanding avian flu collaboration in November when they mentioned the appearance of a strange new virus. Soon, he was jetting off to Singapore to see patients there who presented with symptoms of the same mysterious germ.

Name a major disease outbreak anywhere in the world in the last 20 years—SARS, Ebola, Zika—and chances are Callahan, 57, was there (in his biocontainment suit, of course). A stint working in a refugee camp in the Democratic Republic of the Congo during the 1990s convinced