CDC Director Dr. Rochelle P. Walensky issued guidelines for COVID-19 boosters, clearing the way for tens of millions of U.S. citizens to obtain a third dose of the Pfizer-BioNTech COVID-19 vaccine.

While FDA and the Advisory Committee on Immunization Practices (ACIP) reached broadly similar conclusions regarding booster doses for seniors and high-risk individuals, Walensky went further. A CDC statement also recommends boosters for people 18 to 49 with underlying medical conditions and people 18 to 64 with a high risk of occupational or institutional exposure.

The eligible underlying medical conditions range from having a high body mass index and a history of smoking to HIV and cancer.

In its most recent meeting, ACIP expressed reservations about providing a booster dose to people with a high risk of occupational or facility-based exposure. The committee, however, voted nine to six to back boosters for individuals aged 18 to 49 with underlying health conditions.

Walensky said CDC would review data related to the Moderna and J&J vaccines related to their use as boosters. Both companies have released early data suggesting that boosters of their vaccines offer a substantial boost in immune protection.

CDC has stressed that although boosters can enhance protection against the Delta variant, a more important goal is continuing vaccinating the unvaccinated and partially vaccinated.

“While today’s action was an initial step related to booster shots, it will not distract from our most important focus of primary vaccination in the United States and around the world,” Walensky said in a statement.