Following days of lengthy debate among vaccine experts, booster shots of the Pfizer/BioNTech Covid-19 vaccine can now be officially administered to some adults in the U.S. Early Friday morning, CDC Director Dr. Rochelle Walensky diverged from the agency's independent vaccine advisers to recommend boosters for a broader group of people -- those ages 18 to 64 who are at increased risk of Covid-19 because of their workplaces or institutional settings -- in addition to older adults, long-term care facility residents and some people with underlying health conditions.