WASHINGTON — Pfizer and Moderna say the Food and Drug Administration have opened up COVID-19 booster shots to all adults, letting them choose another dose of either vaccine.

The move expands the government’s booster campaign to shore up protection and get ahead of rising coronavirus cases that may worsen with the holidays.

There’s one more step: The Centers for Disease Control and Prevention must agree to expand Pfizer and Moderna boosters to even healthy young adults. Its scientific advisers are set to debate on Friday.

If the CDC agrees, tens of millions more Americans could have three doses of protection ahead of the new year.

Earlier in the fall, the FDA and the CDC approved booster shots of the Pfizer, Moderna and Johnson & Johnson vaccines for people aged 65 and up, people who have underlying health conditions that make them susceptible to the virus and those who are at an increased risk of contracting the virus because of their job or living situation.

Regulators later approved plans that allow for the mixing and matching of vaccine brands for booster shots.

The CDC reports that more than 32 million Americans have already gotten a COVID-19 vaccine booster shot.