The Biden administration is attempting to put the U.S. on the path of starting COVID booster shots Sept. 20, but this plan is contingent on approval from the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC). It’s become clear that health experts are torn on the need for additional shots, with scientists from the FDA and the World Health Organization (WHO) recently highlighting the potential risks of rolling out booster doses too soon. At the same time, others say the need for more shots outweighs the risks, as initial vaccine effectiveness appears to wane over time and in the face of the highly transmissible Delta variant. But just how much would a third Pfizer dose actually boost the vaccine’s efficacy?
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Pfizer recently submitted data to the FDA for its booster shot, and the agency released a 52-page presentation highlighting this data on Sept. 15, two days before the FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) is set to meet to potentially approve a third dose. Pfizer cited results from Israel, which has already started to administer booster doses to the general population under its COVID vaccination program.
Israel’s study included more than 1.1 million individuals 60 and older who were eligible for a booster dose between July 30 and Aug. 22, comparing rates of infection and severe COVID between individuals who did and did not receive the additional shot. Those who had received the booster doses were more than 11 times less likely to get infected and more than 15 times less likely to get seriously sick than those who were fully vaccinated but did not get a third shot, raising Pfizer’s efficacy back up to 95 percent for both preventing infection and severe illness.
According to the report, this third dose restored these high levels of protection even in a period when Delta was surging, bringing Pfizer’s efficacy back up to the levels it was in the initial vaccine trials, when the Alpha variant was dominant. The CDC released a study on Sept. 10 showing that Pfizer’s two-dose series’ effectiveness against severe COVID was significantly affected by the Delta variant. According to the agency’s finding, this vaccine is 80 percent effective amid the current iteration of COVID, dropping from at least 90 percent protection.
“Israel has clearly demonstrated that, in the face of waning immunity, a booster (third dose) program can be implemented safely at a national level and that a booster dose of [Pfizer] is an effective strategy to restore high levels of protection against COVID-19 outcomes (i.e., back to roughly 95 percent) in a period when Delta is the dominant strain,” Pfizer stated in the FDA report.
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Despite releasing Pfizer’s data in its report, the FDA declined to take an official stance on the third shot in a follow-up 23-page document released Sept. 15. According to the agency, there is mixed data on the need for booster doses, as some observational studies have suggested that Pfizer’s original vaccine series diminishes in effectiveness over time, but others have not. Per the FDA, Israel’s data comes from an observational study, which doesn’t have the same standards of a formal clinical trial, meaning that there are “known and unknown biases that can affect their reliability.”
“There are many potentially relevant studies, but FDA has not independently reviewed or verified the underlying data or their conclusions,” the agency wrote in the follow-up document. “Some of these studies, including data from the vaccination program in Israel, will be summarized during the Sept. 17, 2021 VRBPAC meeting.”
The FDA added, “Overall, data indicate that currently US-licensed or authorized COVID-19 vaccines still afford protection against severe COVID-19 disease and death in the United States.”
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