The company said that early data from its booster study showed the level of neutralizing antibodies among clinical trial participants who received a third dose six months after the second was five to 10 times as high as among two-dose recipients.
Fearful the American public would get the wrong message, the F.D.A. and the C.D.C. reacted with an unusual public statement saying, “Americans who have been fully vaccinated do not need a booster shot at this time.” They added, “We are prepared for booster doses if and when the science demonstrates that they are needed.”
Typically, the F.D.A. would authorize use of a booster, perhaps after a meeting of its outside advisory committee. Then the C.D.C., which has its own advisory committee, would need to formally recommend it, Dr. Offit said.
But if the F.D.A. fully licenses a vaccine, doctors would have vastly more leeway to prescribe a booster for their patients. Some health experts expect that Pfizer could receive that approval by this fall.
At the C.D.C. advisory panel’s meeting Thursday, Dr. Cohn, the medical officer for the vaccine division, suggested that it might be possible to offer booster shots to those with weakened immune systems through an investigational study or other avenues, without waiting for the F.D.A.
Dr. Camille Kotton, an infectious disease expert with Massachusetts General Hospital, told the panel that some patients, especially those who are more educated or “empowered to take care of their own health care,” are managing to get a third dose on their own, despite the lack of a green light from the government.
“Many have taken matters into their own hands,” she said. “I am concerned about them doing this kind of in an unsupervised fashion,” she said, while doctors’ hands are tied because of the lack of regulatory approval.