New studies and a large coronavirus outbreak in Massachusetts bring into question reassuring assertions by US officials about the way the novel virus spreads.
So far, emphasis has been that the virus is spread mainly by people who are already showing symptoms, such as fever, cough or difficulty breathing. But it appears that a Massachusetts coronavirus cluster with at least 82 cases was started by people who were not yet showing symptoms, and more than half a dozen studies have shown that people without symptoms are causing substantial amounts of infection.