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.
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, said Dr. Cheryl Bettigole, the health commissioner. Health officials believe the recent spike is being driven by the highly transmissible BA.2 subvariant of omicron, which has spread rapidly throughout Europe and Asia, and has become dominant in the U.S. in recent weeks.
