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The US Food and Drug Administration is unlikely to ask its outside vaccine advisers to weigh in on whether the agency should authorize Pfizer Covid-19 boosters for all adults, a source familiar with the situation told CNN.

Pfizer applied to the FDA for emergency use authorization on November 9 to make all adults eligible for boosters. Processing that request could be faster if the agency does not wait for members of the Vaccines and Related Biological Products Advisory Committee to meet.

Allowing boosters for all adults has been controversial, as some FDA vaccine advisers are concerned about the risk of myocarditis – inflammation of the heart muscle – a rare side effect that occurs mainly in young men.

The source said “it’s unlikely there is going to be a meeting” of the outside advisers and that “there has been no discussion of a meeting” to discuss Pfizer’s application.

In a statement, the FDA said the agency “will determine whether to hold a meeting of the advisory committee …  following its initial review of the information submitted.” 

When the FDA’s vaccine advisory panel convened last month, the chairman of the committee appeared to lay the groundwork for the group to not reconvene every time there was a decision to be made about booster eligibility.

Dr. Arnold Monto, the acting chairman of the advisory committee, asked an FDA official who was present “about how we can get a little more flexibility so we don’t have to meet and discuss every time we want to go down in age group.”

Monto added in an interview with CNN that as new booster data comes in, several steps must be taken to reconvene the committee.

“In a dynamic situation, it’s very cumbersome to be convened – we have to be screened every time for conflicts of interest and everything else that’s needed to have a meeting – all the legal niceties,” he said. “Our role is to advise on overall policy and to leave the details to the FDA because one, we are advisory, and two, we cannot, the way we are set up, respond quickly to changing circumstances.”

If the FDA authorizes boosters for all adults, the US Centers for Disease Control and Prevention’s external panel of vaccine advisers will meet to review the plan, a federal official said.

“If FDA authorizes it, [the Advisory Committee on Immunization Practices] will be meeting as they have met for everything on Covid vaccines since the beginning in December 2020,” the official said.

CDC Director Dr. Rochelle Walensky would need to sign off on the agency’s final recommendation.

“Dr. Walensky is supportive of using vaccine boosters to protect Americans from COVID-19 when medically necessary and eagerly awaits the opportunity to review data related to Pfizer boosters for those 18 years and older,” a CDC spokesperson told CNN in an email. “Any decision will come after a thorough review of the science, and consultation with internal and external advisors.”

A rocky start

Boosters have had a rocky start in the United States.

In mid-August, President Joe Biden announced “a plan for booster shots to every fully vaccinated [adult] American.” He said that, pending approval by the FDA and the US Centers for Disease Control and Prevention, the booster program would begin during the week of September 20.

A few days later, Pfizer sought the FDA’s approval for booster doses for everyone age 16 and older who were at least six months past their second shot.

But vaccine advisers objected, and instead the FDA authorized Pfizer boosters for a more limited group of adults who are six months past their second shot, including the elderly and those at high risk for developing severe Covid-19. The FDA also authorized boosters for Moderna vaccine recipients in these categories, and for all Johnson & Johnson recipients.

In the minutes of an FDA vaccine advisory committee meeting last month, it was noted that “many” of the advisers were “uncomfortable” lowering the age for boosters below age 40 or 50 “until there are more data on myocarditis.”

Dr. Paul Offit, a member of the FDA vaccine advisory committee, said it would be best for the FDA and the CDC to bring Pfizer’s current application to their advisers.

“I think we need to be transparent about this decision, and the best way for us to be transparent is to hold advisory committee meetings at both the FDA and the CDC so the public can hear the discussion about why this an important thing to do,” he said.

He added that at these meetings, which are public, the data could be laid out.

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“I think we need to show why a booster dose is clearly of benefit to 18-29 year-olds, because if it’s not clearly of benefit, we have to consider the fact that myocarditis was a second dose phenomenon and may also be a third dose phenomenon. Do the benefits clearly and definitively outweigh risks for 18-29 year old?” Offit said.

Monto, the FDA vaccine commitee’s acting chair, said there is a precedent for FDA opting not to consult the vaccine advisory committee on certain decisions.

He said members of the committee meet “at the discretion of the FDA. They are only advisory, and there is a history of [the committee] not meeting over points in which the FDA does not feel they need the advice of the committee.”

CNN’s Amanda Sealy, Danielle Herman and Justin Lape contributed to this report.