In times of emergency, public officials live in fear of not doing enough. But sometimes doing nothing is the right answer. And sometimes doing something makes the problem a lot worse.

An example is the decision to shut down elective surgery in U.S. hospitals and ambulatory clinics. On March 14, Surgeon General Jerome Adams urged a halt in such procedures out of concern they’d spread the coronavirus and strain hospital capacity. On March 18, the Centers for Medicare and Medicaid Services released guidance to limit “elective...