The infections in Dadi Village, a corn farming community tucked between verdant hills in China’s remote southwest, started in early December when a handful of young people returned from jobs in big cities. The nearest hospital was an hour away, and few could afford the $7 bus fare there. The village clinic is not equipped with oxygen tanks or even an oximeter to detect if someone’s blood is dangerously deprived of oxygen. It quickly ran out of its stockpile of five boxes of fever medicine, so officials told sick residents…