By Stephanie Stahl

PHILADELPHIA (CBS) — An FDA panel now recommends a booster of Johnson & Johnson’s COVID-19 vaccine, citing growing concerns that Americans who got the single-dose shot aren’t as protected as those who received two shots of either Moderna or Pfizer. The panel is also considering mixing and matching booster shots.

It’s a little confusing and it appears we’re going to have different dosing and timing recommendations for booster shots. That still hasn’t been officially finalized.

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An FDA advisory panel voted unanimously to recommend a booster for the Johnson & Johnson COVID vaccine two months after the initial shot.

“We want to provide optimal protection against COVID and we know that a booster dose will do that,” Penny Heaton, with Johnson & Johnson, said.

On Thursday, the panel recommended Moderna’s smaller dose booster for Americans over 65, or at high risk, at least six months after the second dose. The same groups are now eligible for the Pfizer booster.

The timing for the J&J booster is shorter, two months instead of six, because its protection is substantially lower than mRNA vaccines.

“Boosting J&J with either Pfizer or Moderna does even better for boosting antibodies,” Penn Medicine Dr. John Wherry said.

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Dr. Wherry is the Director of Penn’s Institute of Immunology. He says there is limited early evidence that mixing vaccines from different manufacturers for a booster shot is safe and can further enhance the immune response.

“Every combination seems to have an advantage of boosting your antibodies levels,” Wherry said.

The FDA panel is reviewing mixing and matching shots — nine different combinations have been studies. If the FDA formally approves the advisory recommendations, the final authorization for the boosters will come from the CDC.

“Sometime in the first couple of days of November, we very likely will get a recommendation from the CDC,” Dr. Anthony Fauci said.

Remember, everything being considered now concerns booster shots. They’re important for the elderly and people who have medical conditions.

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But for everybody else, the only thing you need to worry about is being fully vaccinated.

Stephanie Stahl