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An advisory panel to the US Food and Drug Administration voted unanimously on Friday to recommend a Johnson & Johnson booster for all adults, to be given at least two months after their primary shot.

It’s one of several moving parts in the nation’s vaccination campaign, which involves decisions that are still pending on boosters, mixing and matching vaccines, and shots for children 5 to 11 years old.

Here’s what we know, and what’s still coming.

What was the booster argument for Johnson & Johnson?

The FDA panel evaluated the Johnson & Johnson booster based on data from a large clinical trial that suggested a second shot, given two months after the primary dose, boosted the efficacy against symptomatic COVID-19 to 94 percent in the US. That would put the vaccine in the same efficacy range as the Moderna and Pfizer mRNA vaccines.

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Unlike with the Moderna and Pfizer vaccines, researchers don’t think the immune response from the J&J vaccine wanes over time. So the argument to administer a J&J booster isn’t about getting antibody levels back up after months of decline — it’s about increasing the initial antibody response, which could make the vaccine more effective.

Did the FDA panel discuss a Johnson & Johnson booster dose at six months after the primary shot?

Johnson & Johnson provided early data to the FDA that showed a booster given six months after the primary dose boosted antibody levels, but the panel declined to make an additional recommendation for a booster at that interval. The six-month study included fewer than 20 participants and did not include efficacy data, unlike the larger two-month booster trial.

Several panelists acknowledged that millions of Americans who received the J&J vaccine have likely passed the two-month interval, since the vaccine was authorized in the US in February.

What happens next?

The FDA is expected to announce its decision on the Johnson & Johnson booster by next week. The FDA typically follows the recommendations of its panels, but it isn’t required to. If the FDA agrees, another committee convened by the Centers for Disease Control and Prevention, scheduled for late next week, will offer more specifics on who should get the booster.

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What was the argument for Pfizer and Moderna boosters?

Moderna and Pfizer have advocated for booster doses by citing waning antibody levels over time — a measure that may indicate lower efficacy.

Pfizer was up first for a review of its booster data in September, and the FDA’s advisory panel said there was not enough evidence to support boosters for the general public. Instead, it recommended — and the FDA later authorized — a third dose of the vaccine for those 65 and older or at high risk of severe COVID-19. This week, the panel voted to recommend the Moderna booster under the same criteria and categories.

The Moderna booster would contain half the active mRNA ingredient of shots used in the primary two-dose series.

The FDA panel discussed mixing and matching boosters. What did they say?

Perhaps the most anticipated conversation was on mixing and matching booster shots, following a recent study conducted by the National Institutes of Health. Although the committee did not vote on the matter Friday, the discussion provided some insights.

One challenge is that the age groups for booster eligibility may differ among the three vaccines — a situation likely to confuse the public even more. But some committee members said mixing and matching would allow for more flexibility in the actual delivery of boosters, since people would not need to find specific providers based on the vaccines they offer.

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Dr. Ofer Levy, a physician and principal investigator at Boston Children’s Hospital, said some Americans are already “taking matters into their own hands,” so a recommendation is needed soon.

“I’m reading in the media that people are getting boosters or mixing different products through their primary care providers or by not revealing what they had before,” he said. “I think it is a matter of some urgency for FDA to help sort out what is admittedly a complicated and challenging scenario; but we can’t hide from it.”

Can adolescents get a booster shot?

Not yet. Health agencies in the US are so far only considering boosters for adults.

There isn’t a COVID vaccine available for kids under 12. Is anyone close to an authorization?

Yes. Pfizer asked the FDA on Oct. 7 to clear a version of its vaccine made for children ages 5 to 11. The FDA expects its advisory committee to issue a recommendation during a meeting on Oct. 26.

Moderna applied in June for FDA authorization for kids 12 to 17. What’s happening with that?

The FDA has delayed its decision on allowing adolescents 12 to 17 to receive the Moderna vaccine, according to a report from the Wall Street Journal. Anonymous sources told the WSJ that the agency is reviewing whether there is a risk of a rare inflammatory heart condition, following warnings from Finland, Sweden, Denmark, and Norway. Meanwhile, the Pfizer vaccine has been available to adolescents 12 to 15 years old since May.


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