Attempts to slow the spread of the novel coronavirus are exposing a soft underbelly of the American economy: In our advanced industrialized nation, about 30 million people, or around a quarter of all workers, don’t get paid when they have to take time off work to nurse an illness. These are often the same workers with little to no financial cushion and minimal work-from-home flexibility, which means they’re likelier to stay on the job, accelerating the spread of a contagion.