Contrary to my initial expectations, the spread of the COVID-19 coronavirus around the world is not following the relatively benign trajectories experienced in China outside of Wuhan and Hubei province, and in South Korea, Singapore, and the rest of Asia. Instead, across Europe – and very likely in the United States, too – the spread of the virus increasingly resembles the path it took in Hubei.

This threatens both medical and economic disaster. But while it may be too late for policymakers to avert a public-health crisis, it is still possible to implement the fiscal and monetary me...