The agency also greenlit a "mix and match" approach to boosters — that is, giving a booster shot from a different vaccine maker than the initial vaccination. For example, a person originally vaccinated with Johnson & Johnson could receive a booster shot with the Moderna or Pfizer-BioNTech vaccine.
Before providers can start administering the shots, the Centers for Disease Control and Prevention must sign off. An advisory panel is meeting Thursday to discuss the boosters, and CDC Director Dr. Rochelle Walensky is expected to issue official recommendations shortly after.
The CDC advisory panel is also expected to weigh in on mixing and matching.
The authorizations and increased flexibility on which vaccine people can receive as a booster will increase access to the shots, experts say.
"From a public health perspective, there’s a clear need in some situations for individuals to receive a different vaccine," Dr. Amanda Cohn, chief medical officer on the CDC’s Covid-19 Vaccine Task Force, said during Friday’s FDA advisory committee meeting meeting.
Cohn gave the example of a women in her 30s who may have received the Johnson & Johnson shot before it was discovered the vaccine was linked to a small but increased risk for rare blood clots. A mix-and-match approach would allow that woman, Cohn said, to choose a different type of vaccine for her booster.
It could also make it easier to administer boosters in places such as long-term care facilities. "It would allow a pharmacy to go into a nursing home and only have a single vaccine product to boost individuals who received either Moderna or Pfizer" or the Johnson & Johnson vaccine, Cohn said.
Last week, the National Institutes of Health released a study finding that mixing and matching vaccines was safe and effective, with any combination leading to higher antibody levels. The study also suggested that Johnson & Johnson recipients could particularly benefit from a boost with an mRNA vaccine: Giving either a Pfizer or Moderna booster to a person who previously received Johnson & Johnson increased a person's antibody response 50-fold.
The FDA’s action didn’t include a recommendation for any particular combination of boosters, even though the NIH data presented last week showed that extra mRNA doses sparked a stronger antibody response than a second Johnson & Johnson dose. At a Wednesday press briefing, Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said the agency wouldn’t commit to any particular combination until there was additional data showing which was the most effective.
For people who initially got Moderna, a booster dose is now authorized for adults ages 65 and up, people living in long-term care facilities and adults with underlying medical conditions or who are at high risk of exposure to the coronavirus because of their job. Such people would be eligible at least six months after their second shot.
For people who initially got Johnson & Johnson, a booster is authorized for all adults 18 and up at least two months after their first dose.
The booster that they receive does not need to match the original vaccine type.
The FDA previously authorized Pfizer’s booster shots. The people eligible for that shot match the group eligible for Moderna.
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No matter which booster people ultimately get, the idea behind the extra dose is not necessarily to reduce hospitalizations and deaths, but instead to lower the risk of milder illness, said Dr. Greg Poland, director of the Mayo Clinic’s Vaccine Research Group in Rochester, Minnesota.
“The whole notion of a booster is to reduce moderate and mild disease," Poland said. While boosters may lower the risk of severe illness, "the efficacy of the primary series of vaccine is already so high that you’re only adding to that a modicum."
The boosters also likely lower the risk of breakthrough infections and transmission, he added.
It will be up to the CDC to clarify who is eligible for which shot, a job that could be tricky given the existing criteria for people.
Dr. Mark Sawyer, an FDA advisory committee member and an infectious diseases specialist at Rady Children’s Hospital in San Diego and professor of clinical pediatrics at UC San Diego, said on Friday that clear communication from federal health officials on booster eligibility will be key.
“We need flexibility and improved access for everybody, which the flexibility of being able to mix and match will allow,” Sawyer said, adding that the more straightforward the guidance is, the better off the public will be.