WASHINGTON (CBS/AP) —  An influential federal advisory panel on Friday unanimously endorsed Pfizer’s booster shots against COVID-19 only to Americans 65 and over or at high risk for severe disease.

An earlier 16-2 vote rejected Pfizer’s application to offer vaccine booster shots to most Americans. It was a blow to the Biden administration’s plan to shore up people’s protection against the virus amid the highly contagious delta variant.

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Over several hours of discussion, members of the Food and Drug Administration panel of outside experts voiced frustration that Pfizer had provided little data on safety of extra doses. And they complained that data provided by Israeli researchers about their booster campaign might not be suitable for predicting the U.S. experience.

Pfizer’s documents claim that its vaccine loses some protection after six months, but jumps to 95% following a third dose.

“Some believe boosters should be offered to everyone, while others believe they should only be offered to those at highest risk like seniors, or that they may not be necessary for anyone at this time,” WBZ-TV’s Dr. Mallika Marshall says. “There are also those who believe the shots should be redeployed to help nations who are struggling to vaccinate their own citizens, which would help prevent the emergence of new variants.”

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Cambridge-based Moderna has also developed a booster for its vaccine. The biotech company has submitted initial data to the FDA, saying that its booster dose “induced robust antibody responses of more than 40x against the Delta variant.”

White House Chief Medical Adviser Dr. Anthony Fauci said FDA approval for Moderna’s booster may be delayed “at the most a couple of weeks beyond President Joe Biden’s goal to roll out third shots starting Sept. 20.

Moderna is also working on a combination COVID and flu booster shot.

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