President Trump says 1.4 million tests for the novel coronavirus will become available this week. That’s welcome news. But officials are about to make a mistake. The president said testing will be limited to people who believe they may be infected. “We don’t want everybody taking this test, it’s totally unnecessary,” he said.

This would make sense if there were a cure. Without one, this strategy won’t curtail either the epidemic or the anxiety associated with it. We will continue to bleed billions of dollars in economic costs...