Left: A map of China shows dense pathways of green dots around the city of Wuhan. Right: A light gray map of the United States is covered with red spikes with different heights and densities.

Featured Image: Right: “How the Virus Got Out,” Designed by Jin Wu, Weiyi Cai, Derek Watkins, and James Glanz, New York Times, March 22, 2020. Left: Data graphic from “U.S. Virus Cases Climb Toward a Third Peak,” Lauren Leatherby, New York Times, October 15, 2020