All adults in the U.S. are now eligible to receive Pfizer’s and Moderna’s Covid vaccine boosters, after the Centers for Disease Control and Prevention authorized the shots for the general public Friday. The move allows an extra dose of protection for tens of millions of fully vaccinated Americans as cases climb and public officials worry the nation could face another surge during the winter.

CDC Director Rochelle Walensky signed off on the booster shots hours after the agency’s independent panel of vaccine scientists unanimously endorsed opening up eligibility to everyone 18 and older at least six months after they received their second dose.

The Food and Drug Administration had authorized both companies’ vaccine boosters for all U.S. adults earlier Friday.

“After critical scientific evaluation, today’s unanimous decision carefully considered the current state of the pandemic, the latest vaccine effectiveness data over time, and review of safety data from people who have already received a COVID-19 primary vaccine series and booster,” Walensky said in a statement Friday evening.

“Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays. Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose,” Walensky said.

The CDC also said people over the age of 50 should get booster shots, a stronger recommendation for that age group than before. The panel previously limited its strongest guidance to people over 65 and other people with high risk.