Jason McLellan was wandering around a ski shop of Utah’s Park City Mountain Resort, waiting for his new snowboarding boots to be heat-molded to his size-nine feet, when his smartphone rang. It was Barney Graham, deputy director of the National Institute of Allergy and Infectious Diseases Vaccine Research Center.

Two days earlier, the World Health Organization had announced that several unidentified pneumonia-like cases had been reported in Wuhan, China. People were fatigued and feverish, with dry coughs and headaches. These symptoms weren’t unusual for early January, but some people were short of breath, and a few felt like they’d been hit by a train.

This duo was part of a small band of government and university scientists who had spent