The Food and Drug Administration on Wednesday authorized for emergency use a booster dose of the Pfizer-BioNTech vaccine for those aged 65 and older, as well as those aged 18–64 who are at high risk of severe COVID-19. The third dose of the mRNA-based shot is authorized to be administered at least six months after the first two doses of the vaccine. A third population eligible for the dose under the amended FDA emergency use authorization (EUA) are those aged 18-64 “whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk of serious complications of COVID-19 including severe COVID-19.” This third category includes “health care workers, teachers, and day care staff, grocery workers, and those in homeless shelters or prisons,” among others, Acting FDA Commissioner Janet Woodcock said in a statement. The Centers for Disease Control and Prevention (CDC) is expected to issue guidance on the distribution of the Pfizer …