New research suggests that many people have had the coronavirus without any symptoms of it. If confirmed, experts hope that the virus will be much less deadly than they feared. It also means, however, that it is impossible to know who may be contagious. That would complicate decisions on when return to work or to school. Over the past week, reports of infections without symptoms have come from a homeless shelter in Massachusetts and pregnant women at a New York hospital. Other “silent” infections were reported in California, several European countries and even on a United States Navy aircraft carrier.