For more than a year, Chinese officials have beat back the coronavirus with a tried formula: Strict lockdowns at the sites of outbreaks. Lengthy quarantines for travelers. And citywide testing when new cases appear.But an outbreak of the fast-spreading Delta variant could challenge China’s zero-tolerance approach toward new infections.In the outbreak, centered in the eastern city of Nanjing, about 200 cases have been reported as of Friday. But infections have spread rapidly, with patients emerging in at least six Chinese provinces and the capital, Beijing, in just three weeks.As officials move to contain the spread, the highly …
