China is resolutely sticking with its zero-tolerance approach to COVID-19, even as the delta variant continues to penetrate its formidable defenses. Officials are implementing increasingly aggressive measures — ranging from internal travel restrictions, snap lockdowns and mass testing of millions — in an attempt to rein in the virus.

Yet more parts of the country are grappling with outbreaks than at any time since the deadly pathogen first emerged in Wuhan in 2019. Hundreds of locally transmitted infections have been found in about two thirds of its provinces.

The last of the major "COVID zero" holdouts, China is becoming ever more isolated, and its unpredictable curbs are beginning to disrupt the world’s second-largest economy. How long can the vast nation maintain its strategy as the rest of the world learns to live with COVID-19, and what factors might force the country to re-open?