Pfizer and BioNTech on Thursday announced they will seek FDA authorization of a booster shot of their Covid-19 vaccine, but several infectious disease experts said booster shots may not be necessary—at least not yet.

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Pfizer-BioNTech will seek authorization for a booster shot

Pfizer and BioNTech in a statement said they've seen "encouraging data" from an ongoing trial of their booster shot, which is administered as a third vaccine dose approximately six months after a patient's second dose. The companies intend to submit their data to FDA "in the coming weeks."

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Mikael Dolsten, from Pfizer, told the Associated Press that the trial suggests antibodies in those receiving a booster shot increase five- to 10-fold compared to their second dose.

Pfizer and BioNTech said that, while protection against severe Covid-19 remains strong in fully vaccinated people six months after vaccination, protection against more minor cases of Covid-19 started declining at the end of that time period. Waning immunity in conjunction with the rise of new variants "are key factors driving our belief that a booster dose will likely be necessary to maintain highest levels of protection," the companies said.

The companies specifically pointed to data from Israel, where health officials have estimated Pfizer-BioNTech's vaccine provided just 64% efficacy against symptomatic infection during an outbreak driven by the delta coronavirus variant.

However, other studies have found higher efficacy rates against the delta variant, the New York Times reports—and even in the Israeli study, the vaccine still provided 94% protection against severe Covid-19.

Pfizer and BioNTech added they are preparing a clinical trial to start in August of a modified Covid-19 vaccine specifically aimed at the delta variant, if it's necessary.

Are booster shots needed yet?

Some experts and health officials have said Covid-19 booster shots are not necessary—at least yet—and that the main focus should be on getting more people fully vaccinated.

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After Pfizer and BioNTech's announcement, FDA and CDC issued a joint statement saying that fully vaccinated Americans "do not need a booster shot at this time," adding that the agencies are working through a "science-based, rigorous process" to determine when and if booster shots will be necessary.

That process will include data from pharmaceutical companies "but does not rely on [that] data exclusively," the agencies said, and any decision to approve booster shots will occur when "the science demonstrates that they are needed."

Still, health officials have in the past indicated that booster shots may be needed eventually. For instance, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, in May noted that natural immunity to other coronaviruses "is generally not lifelong." He added, "We know that the vaccine durability of the efficacy lasts at least six months, and likely considerably more, but I think we will almost certainly require a booster sometime within a year or so after getting the primary."

But some infectious disease experts responded to the Pfizer and BioNTech announcement by suggesting that, even if boosters are eventually necessary, their time hasn't yet arrived.

Céline Gounder, an infectious disease specialist at Bellevue Hospital Center in New York, said there is "really no indication" that booster shots are needed yet. "In fact, many of us question whether you will ever need boosters," she said.

Monica Gandhi, a professor of medicine and infectious disease specialist at the University of California, San Francisco, said booster shots aren't immediately necessary except for the very elderly and those with compromised immune systems.

Gounder added that every unvaccinated person in the world provides the coronavirus with another chance to mutate into a more dangerous variant.

"If we're worried about variants, our best protection is to get the rest of the world vaccinated, not to hoard more doses to give third doses of mRNA vaccines to people here in the U.S.," she said. (Neergaard, Associated Press, 7/9; Sullivan, The Hill, 7/8; Walker, Wall Street Journal, 7/8; Weintraub, USA Today, 7/8; Axios, 7/8; Mandavilli, New York Times, 7/8; Gonzalez, Axios, 7/8)