A U.S. Centers for Disease Control and Prevention (CDC) advisory panel on Thursday recommended a booster shot of the Pfizer and BioNTech COVID-19 vaccine for Americans age 65 and older and some adults with underlying medical conditions that put them at risk of severe disease.

But the panel declined to recommend boosters for younger adults, including health care workers, who live or work in institutions with high risk of contracting COVID-19, which could narrow the scope of the U.S. Food and Drug Administration's emergency use authorization issued on Wednesday.

The guidelines voted on by the CDC's Advisory Committee on Immunization Practices still need to be signed off on by agency Director Rochelle Walensky. The recommendations are not binding, and states and other jurisdictions could disregard them and use other approaches to administering the booster shots.