An advisory panel of the US Centers for Disease Control and Prevention (CDC) on Thursday decided not to recommend boosters for younger adults, including healthcare workers, who live or work in institutions with high risk of contracting COVID-19, Reuters news agency reported on Friday.

The panel has only recommended a booster shot of the Pfizer (NYSE:PFE)/BioNTech (Nasdaq:BNTX) COVID-19 vaccine for Americans aged 65 and older and some adults with underlying medical conditions that put them at risk of severe disease.

For now, the panel has rejected additional doses for groups including healthcare workers, teachers and residents of homeless shelters and prisons, in part because of the difficulty of implementing such a proposal.

In addition to older Americans, the committee also recommended the booster shots for all adults over 50 with underlying conditions, as well as some 18- to 49-year-olds with those conditions, based on their individual risk profile. Those conditions include cancer, diabetes, certain heart conditions and chronic kidney disease and lung disorders.

The recommendations only cover people who received their second Pfizer/BioNTech shot at least six months earlier. This group is currently about 26 million people, including 13 million aged 65 or older, the CDC said.