How China's Nanjing airport led to lockdowns in 3 provinces amid Covid surge

• China is battling a Covid surge again owing to the Delta variant of the virus. A coronavirus cluster that emerged in the Chinese city of Nanjing has now reached five provinces and Beijing, forcing lockdowns on hundreds of thousands of people as authorities scramble to stamp out the worst outbreak in months. China tested all of Nanjing’s 9.2 million people twice. The outbreak is geographically the largest in several months, challenging China's aggressive containment efforts which have relied on mass testing, lockdowns, and swift contact tracing.