Federal health officials hope a straightforward boosters-for-all policy will prompt millions more people to get the shots before they travel or gather with friends and family over the holidays. Many are concerned about the worsening picture as winter approaches. After new cases dipped to almost 69,000 on Oct. 25 — their lowest point in months — they began climbing again, with the seven-day average rising 40 percent to more than 96,000 on Thursday.

The final piece of the booster-policy overhaul fell into place early Friday evening when Rochelle Walensky, director of the Centers for Disease Control and Prevention, accepted two unanimous recommendations from the agency’s independent experts. The Advisory Committee on Immunization Practices said anyone 18 and older may get a booster and — to stress the urgency of increasing protection for the most vulnerable age group — anyone 50 and older should make sure they get one.

“Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose,” Walensky said in a statement. “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.”