FILE - A sign requiring masks as a precaution against the spread of the coronavirus on a store front in Philadelphia, is seen Feb. 16, 2022. Philadelphia is reinstating its indoor mask mandate after reporting a sharp increase in coronavirus infections, Dr. Cheryl Bettigole, the city's top health official, announced Monday, April 11, 2022. Confirmed COVID-19 cases have risen more than 50% in 10 days, the threshold at which the city's guidelines call for people to wear masks indoors. (AP Photo/Matt Rourke, File)
Philadelphia became the first major U.S. city to reinstate its indoor mask mandate on Monday after reporting a sharp increase in coronavirus infections, with the city’s top health official saying she wanted to forestall a potential new wave driven by an omicron subvariant.