The delta variant is challenging China’s costly strategy of isolating cities, prompting warnings that Chinese leaders who were confident they could keep the coronavirus out of the country need a less disruptive approach.

As the highly contagious variant pushes leaders in the United States, Australia and elsewhere to renew restrictions, President Xi Jinping’s government is fighting the most serious outbreak since last year’s peak in Wuhan.

The ruling Communist Party is reviving tactics that shut down China: Access to a city of 1.5 million people has been 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 from abroad helped to contain last year’s outbreak and has kept China largely virus-free. But its impact on work and life for millions of people is prompting warnings that China needs to learn to control the virus without repeatedly shutting down the economy and society.

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