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An advisory panel to the US Food and Drug Administration voted Thursday to recommend Moderna’s booster shot for people 65 and older, adults at high risk of severe COVID-19, and adults who have increased COVID risk at their workplace, at least six months after their second dose.

The recommendation mirrors the criteria and categories used in the authorization of Pfizer-BioNTech booster shots last month, and it puts Moderna one step closer to receiving clearance for its booster from the FDA. Yet some questions remain.

What happens next?

After the scientific panel’s recommendation, the FDA is expected to announce its decision on the Moderna booster shot by early next week. The FDA isn’t required to follow its panel’s recommendation, but typically does.

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If the FDA follows the panel’s advice, another advisory panel convened by the Centers for Disease Control and Prevention, scheduled for later next week, will offer more specifics on who should get a Moderna booster. The CDC will have the final word on that.

Is Moderna’s booster the same vaccine that was used in its original two-shot series?

Not exactly. Moderna asked the FDA to authorize a booster shot that contains half the active ingredient of its already authorized vaccine. The booster would have 50 micrograms of messenger RNA, whereas each dose in the primary series contains 100 micrograms.

That makes things slightly more complicated. The FDA previously authorized a Moderna booster shot — at the full 100-microgram dosage — for transplant patients and other individuals who did not mount a strong immune response to the original vaccine series. (It was not immediately clear if that guidance could change.)

How did the FDA panel decide who should get the Moderna booster?

The panel evaluated Moderna’s booster shot application based on the same criteria it used when issuing a recommendation for a Pfizer-BioNTech booster in September. That decision set a clear precedent. Although Pfizer — and the Biden administration — originally wanted booster shots available to all Pfizer recipients, regardless of age, whether they were immunocompromised, or at risk of developing severe COVID-19, the FDA only authorized the booster shots for individuals:

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  • 65 and older.
  • 18-64 years old and at high risk of severe COVID-19.
  • 18-64 years old whose job puts them at high risk of serious complications of COVID-19, including health care, school, and grocery store workers.

I’m eligible for a booster shot. Can I mix and match vaccines?

It’s a question many are asking, especially after the release of a preprint study that suggests the strategy may lead to a similar or stronger immune response than sticking with the same vaccine. But the official answer, for now, is no. The FDA advisory panel may discuss the mix-and-match concept on Friday, but it won’t make a decision.

STAT reported that drug makers typically ask regulators for approval of the use of their shots, but they’re not likely to ask to have a rival’s vaccine used as a booster.

The Pfizer booster has been authorized for certain individuals, and Moderna is now one step closer. What about Johnson & Johnson?

A Johnson & Johnson booster is up for review by the same FDA panel of scientific advisers on Friday. The group is expected to issue a recommendation to the agency by the end of the day.

Unlike the two-shot vaccines from Pfizer-BioNTech and Moderna, Johnson & Johnson’s vaccine is supposed to require only one shot. A presentation slide shown during Thursday’s panel meeting suggested that on Friday the committee will vote on whether a J&J booster should be administered two or six months after the primary dose.

Material from Martin Finucane of the Globe staff and Globe wire services was used in this report.


Anissa Gardizy can be reached at anissa.gardizy@globe.com. Follow her on Twitter @anissagardizy8.