BEIJING—The Delta variant is challenging China’s costly strategy of isolating cities. The Chinese regime is struggling with the most serious outbreak since last year’s peak in Wuhan. The Chinese Communist Party (CCP) is reviving tactics that shut down China: access to a city of 1.5 million people cut off, flights canceled, and mass testing ordered in some areas. That “zero tolerance” strategy of quarantining every case and trying to block new infections impacted the work and life of millions of people. It is prompting warnings that the CCP needs to learn to control the virus without repeatedly shutting down the economy and society. Zhang Wenhong, a Shanghai doctor who became prominent during the Wuhan outbreak, suggested in a social media post that the CCP’s strategy could change. “We will definitely learn more” from the ongoing outbreak, he said. “The world needs to learn how to coexist with this virus,” wrote …