Pfizer and BioNTech on Tuesday said they've requested FDA to expand its authorization for booster doses of the companies' Covid-19 vaccine to include anyone age 18 and older, a move that would significantly increase the number of Americans eligible for a booster shot.

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Pfizer and BioNTech request booster authorization for all adults

As it stands, the Pfizer-BioNTech vaccine booster is authorized for mRNA vaccine recipients who are 65 years or older, as well as those over 18 who are at high risk of severe Covid-19 or are at high risk of exposure to Covid-19 because of their profession. (It is also available to adults who previously received the single-dose Johnson & Johnson vaccine.)

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The two companies said their new request to broaden that authorization was based on a Phase 3 trial involving more than 10,000 participants that found booster shots were safe and had a 95% efficacy rate against symptomatic Covid-19 compared to those who had received only two doses of the vaccine.

FDA is expected to grant the companies' request, the New York Times reports, and it isn't expected to convene its advisory panel to discuss the need to do so.

If FDA elects to expand Pfizer-BioNTech's authorization, CDC would then need to officially recommend the shots before they could be widely administered, NBC News reports.

What experts say about making booster shots widely available

In September, when FDA's advisory committee met to discuss authorizing booster shots, the committee voted against Pfizer and BioNTech's request to expand booster shots to all adults, citing a lack of data showing that boosters were necessary.

Some experts say that, since then, more data has emerged strengthening the case for boosters.

Peter Chin-Hong, an infectious disease doctor at the University of California, San Francisco, said he has grown more open to boosters as he's had personal experience with patients experiencing breakthrough infections and has seen better data on the waning effectiveness of the initial, two-dose vaccine regimen.

"I think a lot of people are actually changing their minds a little bit from the initial thought of 'no boosters are needed,'" he said.

While the two-dose regimen remains very effective at preventing hospitalizations and death for younger people, protection against milder infection is also important, Chin-Hong said.

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"It is a drag to even get an infection right now, meaning you have to tell everybody you are in contact with, you stay home from work and school," he said.

Nahid Bhadelia, director of the Boston University Center for Emerging Infectious Diseases Policy and Research, said that "there's some stronger data" in favor of booster shots than there was in September.

"I think that the boosters now seem to look like they may help prevent severe disease for a lot more people than we thought previously," she said.

Earlier this month, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, noted that data from Israel—where booster shots are available to everyone ages 12 and older—has shown "rather dramatic" drops in severe Covid-19 cases, hospitalizations, and deaths.

One study from Israel published in The Lancet in October looked at around 730,000 people who received a booster shot in August or September compared to those who received just two doses of the Pfizer-BioNTech vaccine. It found that those who received boosters experienced a 93% reduced risk of hospitalization, a 92% reduced risk of severe Covid-19, and an 81% reduced risk of death.

Even so, some experts argue that it's premature to expand booster eligibility.

In an opinion piece for the Annals of Internal Medicine, Ameet Sarpatwari—from Brigham and Women's Hospital and Harvard Medical School—and colleagues argued that the United States should instead focus on getting more people their first shots of a Covid-19 vaccine, increasing access to rapid Covid-19 testing, and deploying vaccines worldwide.

"The probability of higher booster uptake in regions with high initial uptake suggest that the magnitude of additional societal benefit with a booster-for-all policy will be small," the authors wrote.

They argued that the federal government doesn't have the resources to expand booster outreach without undermining efforts to vaccinate the currently unvaccinated and to deploy the vaccine worldwide.

"Tradeoffs are inevitable in both scope and speed of action given limited resources," the authors wrote. "Frequent changes to booster eligibility and requirements also divert resources from simpler strategies that could be more effective for pandemic control." (Reyes, Axios, 11/9; LaFraniere, New York Times, 11/9; Miller, NBC News, 11/9; Sealy/Gumbrecht, CNN, 11/9; Hopkins/Armour, Wall Street Journal, 11/9; Walker, MedPage Today, 11/9; Palca, "Shots," NPR, 11/9)