The high-level online meeting, which lasted an hour and involved Pfizer’s chief scientific officer briefing virtually every top doctor in the federal government, came on the same day Israel started administering third doses of the Pfizer-BioNTech vaccine to heart transplant patients and others with compromised immune systems. Officials said after the meeting that more data — and possibly several more months — would be needed before regulators could determine whether booster shots were necessary.
Last week, Pfizer and BioNTech said a booster given six months after the second dose of the vaccine increased the potency of antibodies against the original virus and the Beta variant by five- to tenfold. But antibody levels may not be the best biological measurement of the need for booster doses, according to experts, who say it is no surprise that antibodies would increase after taking a third dose.
“Antibody response is not the only measure of immune protection,” said Dr. Leana S. Wen, a former health commissioner for Baltimore. “There have been multiple studies that suggest these vaccines also stimulate B cell and T cell immunity, so even if there isn’t as much antibody, that doesn’t mean someone isn’t protected.”
In Israel, the government agreed to provide Pfizer with data on its vaccine recipients, and Pfizer has been matching the Israeli data with its own laboratory tests on antibody responses. Some people familiar with the data say that taken together, the two data sets indicate that immunity is waning among the vaccinated after roughly six to eight months, leading to a growing number of breakthrough infections.