FILE - In this March 26, 2021, file photo, a member of the Philadelphia Fire Department administers the Johnson & Johnson COVID-19 vaccine to a person at a vaccination site at a Salvation Army location in Philadelphia. More Black Americans say they are open to taking the coronavirus vaccine amid campaigns to overcome a shared historical distrust of science and government. (AP Photo/Matt Rourke, File)

WASHINGTON (AP) — U.S. health advisers endorsed a booster of Johnson & Johnson’s COVID-19 vaccine Friday, citing concern that Americans who got the single-dose shot aren’t as protected as those given two-dose brands.

J&J told the Food and Drug Administration that an extra dose adds important protection as early as two months after initial vaccination — but that it might work better if people wait until six months later. Unable to settle the best timing, the FDA’s advisory panel voted unanimously that the booster should be offered at least two months after people got their earlier shot.

“I think this frankly was always a two-dose vaccine,” said FDA adviser Dr. Paul Offit of Children’s Hospital of Philadelphia. “It would be hard to recommend this as a single-dose vaccine at this point.”

The FDA will use its advisers’ recommendations to decide whether to authorize boosters for both J&J and Moderna. Next, the Centers for Disease Control and Prevention would rule on who should roll up their sleeves.

The vast majority of the 188 million Americans who are fully vaccinated against COVID-19 have received the Pfizer or Moderna options, while J&J recipients account for only about 15 million.

J&J’s vaccine is made with a different technology and on Friday, the company pitched its booster as a way to strengthen a robust vaccine that they said has retained its protective power over eight months. But FDA scientists pointedly challenged that assertion.

“There are data that suggest the effectiveness of this vaccine is actually less robust than the company’s presentation here,” said Dr. Peter Marks, FDA’s top vaccines official. “And that is a finding of concern particularly because that’s been seen in minority communities potentially and others.”

As for its booster, J&J presented results from a large study that found giving a second dose just two months after the first bumped protection against symptomatic COVID-19 to 94% from 70% in U.S. recipients. Giving that booster six months later instead prompted an even bigger jump in virus-fighting antibodies.

But in their own review, FDA scientists noted only a tiny portion of cases involved the delta variant, by far the dominant strain in the U.S. And while FDA’s reviewers found no new safety concerns about a second J&J dose, they noted other shortcomings. J&J followed booster recipients for little more than a month, making it hard to draw conclusions about the durability of protection. Also, FDA scientists stressed they hadn’t had time to independently confirm J&J’s data, which were submitted shortly before the meeting. That’s highly unusual and drew serious concern from the advisory panel.

The J&J vaccine was highly anticipated for its one-and-done formulation. But its rollout earlier this year was hurt by a series of troubles including manufacturing problems and some rare but serious side effects including a blood clot disorder and a neurological reaction called Guillain-Barre syndrome. In both cases, regulators decided the shot’s benefits outweighed those risks.

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