Philadelphia becomes first major US city to reinstate indoor mask mandate

Covid-19 cases have risen more than 50% in 10 days, the threshold at which city's guidelines call for masking indoors

Philadelphia on Monday became the first major US city to reinstate its indoor mask mandate 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 sub-variant.

Confirmed Covid-19 cases had risen more than 50% in 10 days, the threshold at which the city's guidelines called for people to wear masks indoors, said Dr Cheryl Bettigole, Philadelphia health commissioner.