FILE - A doctor loads a dose of Pfizer COVID-19 vaccine into a syringe, Thursday, Dec. 2, 2021, at a mobile vaccination clinic in Worcester, Mass. In January 2022, an influential government advisory panel is considering COVID-19 boosters for younger teens, as the U.S. battles the omicron surge and schools struggle with how to restart classes amid the spike. (AP Photo/Steven Senne, File)