An analysis of serum samples collected as part of routine COVID-19 testing from 16,025 people of all ages at 10 US sites from Mar 23 to May 12 suggests that, while most people had not been infected, at least 10 times more people were probably infected than previously reported, according to a study published today in JAMA Internal Medicine.Two other studies, published today in Morbidity and Mortality Weekly Report, showed low antibody seroprevalence levels in Indiana and Georgia.The JAMA Internal Medicine study, led by researchers from the Centers for Disease Control and Prevention, is the first known US multistate and city-level serosurveillance study.