On april 25th Bloomberg ranked Singapore as the world’s best country in which to weather the pandemic, in part because it had almost no local transmission. Two days later a 46-year-old nurse at Tan Tock Seng Hospital tested positive for the virus, revealing a cluster of dozens of infections. Within a week the government identified other new clusters, including at the airport and port. “We are now on the knife’s edge,” Lawrence Wong, a minister on Singapore’s covid-19 task force, warned on May 11th. “Our community cases can go either way in the next few weeks.”

Much of South-East Asia is similarly poised. Across the region, clusters have been found in places where defences are weakest: hospitals, quarantine facilities and border crossings. Lapses in those places allowed infections to spread more widely. Moreover, the virus has mutated over the past year, and the variants spreading now are more transmissible. That includes b.1.617, first identified in India, which has appeared in Cambodia, Indonesia, Malaysia, Singapore and Thailand.