5 reasons why FDA advisers did not recommend Covid-19 booster shots for everyone - CNN

They did recommend a more limited step: emergency use authorization for people 65 and older, and for people at high risk of severe infection.

Michael Kurilla, an infectious disease specialist at the National Center for Advancing Translational Sciences, said he suspected Pfizer went too far in extrapolating data on older people to a younger population.

"So it's unclear that everyone needs to be boosted, other than a subset of the population that clearly would be at high risk for serious disease," Kurilla said.

Philip Krause, deputy director of the FDA's Office of Vaccines Research and Review, noted that Pfizer was using data that had not been reviewed by experts.

"One of the issues in this is that much of the data that's been presented and being discussed today is not peer-reviewed and has not been reviewed by FDA," Krause said.

Krause, along with another FDA vaccine official, Marion Gruber, signed a paper published The Lancet earlier this week that argued it's too soon to start giving people boosters.

Kurilla noted that Pfizer's studies relied heavily on measurements of antibodies, without looking at other important aspects of immune response.

"It's a little disappointing that there's been very little reporting of the cellular immune responses and an entire focus on the neutralizing antisera," Kurilla said.

Hayley Ganz, a professor of pediatrics at Stanford University Medical Center.

They are worried about younger adults and teens

"We're being asked to approve this as a three-dose vaccine for people 16 years of age and older, without any clear evidence the third dose for a younger person, when compared to an elderly person, is of value," Offit said.

"If it's not of value, then the risks may outweigh the benefits.

"We really don't have enough data yet to know what the risk of myocarditis or pericarditis would be following a booster dose," he said.