In this May 21, 2021 file photo, a person holds a mask while walking outside in Philadelphia. New evidence showing the delta variant is as contagious as chickenpox has prompted U.S. health officials to consider changing advice on how the nation fights the coronavirus. Recommending masks for everyone and requiring vaccines for doctors and other health care providers are among measures the Centers for Disease Control and Prevention is considering, Friday, July 30. (AP Photo/Matt Rourke, File)