How long can we keep this up? It is still very early in the U.S. effort to snuff a lethal pandemic by shutting down much of the economy. But there is a growing question — from workers, the White House, corporate boardrooms and small businesses on the brink — that hangs over what is essentially a war effort against a virus that has already killed more than 9,000 Americans . There is no good answer yet, in part because we don’t even have the data needed to formulate one. Essentially, economists say, there won’t be a fully functioning economy again until people are confident that they can go about their business without a high risk of catching the virus. “Our ability to reopen the economy ultimately depends on our ability to better understand the spread and risk of the virus,” […]