Booster shots of Moderna’s and Johnson & Johnson’s COVID-19 vaccines became available to tens of millions of Americans on Friday, a day after the Centers for Disease Control and Prevention recommended the additional doses for certain people.

Before the CDC’s recommendation was issued, the FDA granted emergency use authorizations for the booster shots. 

People ages 65 and older, along with younger adults who have underlying medical conditions or live or work in high-risk settings, are eligible to receive a booster shot if they were given their second Moderna dose at least six months ago. The recommendations match those for the Pfizer booster, which was authorized last month.

All adults who received the single-shot Johnson & Johnson vaccine at least two months ago are also now eligible for a booster.

Regulators also approved the practice of “mixing-and-matching” vaccines, meaning people can choose a different brand for their boosters than they received initially.

“Some people may have a preference for the vaccine type that they originally received because they did very well with their initial series,” CDC Director Dr. Rochelle Walensky said Friday. “For all three vaccines, this is perfectly fine. And now with 10 months of vaccine experience, some may have an express preference for one booster type over another.”

With the approval of the Moderna and Johnson & Johnson boosters, 70 million Americans are now eligible for additional shots. Another 50 million will become eligible in the coming months, said Jeff Zients, White House COVID-19 response coordinator. 

As of Thursday, 11.6 million Americans had received a booster shot.

Zients said the Biden administration has been preparing for two months for the rollout of boosters. 

“We are ready to get booster shots in the arms of tens of millions of newly eligible Americans,” he declared Friday.

Zients said the U.S. has ample supply of all three vaccines authorized in the country, as well as a well-tested nationwide distribution system. 

The shots will be available at 80,000 locations, including more than 40,000 pharmacies, as well as thousands of doctors offices, community health centers and vaccination sites. 

Walgreens said Friday that the Moderna and J&J booster shots are available now at its stores nationwide. 

CVS said Moderna’s boosters are available at select stores. The company stopped offering the J&J vaccine at its pharmacies in August. 

The Moderna booster uses a dosage — 50 micrograms — that is half of what was given in the two primary shots.

The booster shots are free. No insurance or ID is required. 

Walensky again said, “We will not boost our way out of this pandemic,” adding that no vaccine, even when boosted, is 100% effective.

“So even after you boost, it remains important for us to remain smart about our prevention strategies while we still have over 93% of our counties with high or moderate community transmission,” she said. “Currently around 64 million Americans remain unvaccinated, leaving themselves and their children, their families, their loved ones and communities vulnerable.

Nearly 190 million Americans — 57% of the total population — has been fully vaccinated. About 64 million people who are eligible have not received a single shot.