A health care worker prepares a dose of the Moderna COVID-19 vaccine during a clinic held at the Watts Juneteenth Street Fair in the Watts neighborhood of Los Angeles.

Patrick T. Fallon/AFP via Getty Images

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Patrick T. Fallon/AFP via Getty Images

A health care worker prepares a dose of the Moderna COVID-19 vaccine during a clinic held at the Watts Juneteenth Street Fair in the Watts neighborhood of Los Angeles.

Patrick T. Fallon/AFP via Getty Images

The Food and Drug Administration authorized booster doses of the COVID-19 vaccines made by Moderna and Johnson & Johnson following unanimous votes by a committee of independent advisers backing the boosters last week.

In a related decision, the FDA also authorized boosters that differ from the vaccine originally used to immunize people against COVID-19. So, for instance, a person who got a Johnson & Johnson vaccine could receive one from Moderna or Pfizer-BioNTech as a booster.

The regulatory moves open the gate for boosters to be used more widely. In September, FDA authorized a booster for the Pfizer-BioNTech COVID-19 vaccine.

“The available data suggest waning immunity in some populations who are fully vaccinated,” said Acting FDA Commissioner Janet Woodcock in a statement. “The availability of these authorized boosters is important for continued protection against COVID-19 disease.”

On Thursday, a committee of advisers to the Centers for Disease Control and Prevention is scheduled to meet to discuss COVID-19 vaccine booster shots and make recommendations on their use. The CDC director makes the final call on vaccine guidelines. After the CDC issues its guidance the rollout can begin officially.

A study of the mix-and-match approach funded by the National Institutes of Health found no safety concerns using different vaccines as a boost. The boosts with a mixed vaccine combination were at least as good in stimulating antibodies as matched vaccines, the study found, and in some cases the mixed approach appeared much better.

By blessing the use of a mixed vaccine combination, the FDA makes it easier to give booster shots in nursing homes where residents haven’t all received the same original immunizations.

“From a public health perspective, there’s a clear need in some situations for some individuals to receive a different vaccine,” said Dr. Amanda Cohn, chief medical officer at the CDC’s National Center for Immunizations and Respiratory Diseases, during the FDA meeting Friday.

The decision could also make it easier for a wide range of people to get a booster since any available shot would do.

Dr. Mark Sawyer, a committee member from Rady Children’s Hospital in San Diego, cited ease of access under the mix-and-match approach during the committee’s deliberations. “I’m sold already,” he said, “and that’s because I agree completely with Dr. Cohn’s comments that we need flexibility and improved access for everybody, which the flexibility of being able to mix and match will allow.”

The Moderna authorization covers a booster for people who were immunized with the company’s two-shot vaccine at least six months beforehand and are 65 years and older, 18 to 64 and at high risk of severe COVID-19 or are in the same age group and whose work or institutional exposure puts them at high COVID-19 risk.

The authorization comes after a committee of advisers to the FDA voted 19-0 in support of the booster last Thursday. The scope of the Moderna authorization matches the one FDA gave to Pfizer-BioNTech COVID-19 booster doses in September.

One difference: Moderna’s COVID-19 vaccine booster is half the dose of the initial shots used in its two-shot vaccination — 50 micrograms of mRNA versus 100 micrograms per each initial shot. The Pfizer vaccine uses a third identical dose.

The FDA also authorized a booster dose of the J&J vaccine at least two months after initial immunization for people 18 and older. A study published by the CDC in September that showed the J&J vaccine had effectiveness of around 68% in keeping people out of the hospital for COVID-19 compared with more than 90% for Moderna’s vaccine and about 77% for the Pfizer-BioNTech after about four months.

Several committee members noted that people were getting booster doses and using a mix-and-match approach on their own.

“Many Americans are taking matters into their own hands,” said Dr. Ofer Levy, a professor of pediatrics at Harvard Medical School. “I’m reading in the media that people are getting boosters or mixing different products through their primary care providers, or not revealing what they got before. In the real world, all these kinds of combinations of extra boosters are already happening.”

More than 9 million people have received a Pfizer booster, according to data from the Centers for Disease Control and Prevention. Even before FDA’s authorization, CDC data show that more than 1.6 million people have received a Moderna booster and more than 11,000 another shot of J&J’s vaccine.

Ofer asked the FDA to act quickly: “I think it’s a matter of some urgency for FDA to help sort out what is admittedly a complicated and challenging scenario. We can’t hide from it. And I do think we need to give guidance to the public.”