A key Food and Drug Administration panel on Thursday voted in favor of recommending booster doses of Moderna's COVID-19 vaccine for a large swath of the population.
Members of the Vaccines and Related Biological Products Advisory Committee (VRBPAC) voted unanimously, 19-0.
The agency's vaccine advisory committee said boosters should be recommended for people over 65, people between the ages of 18 and 64 who are at high risk of severe COVID-19, as well as people who are at risk of serious COVID-19 because of their jobs, or living situation.
The population recommended for Moderna's booster is the same population that Pfizer's booster was authorized for last month. About 60 million Americans are now eligible for Pfizer's booster.
The Biden administration has made boosters for all Americans a priority, even though experts are divided on whether the general population will really benefit. Ultimately, the way to end the COVID-19 pandemic is by getting shots to the unvaccinated, rather than boosting those who are already protected.
Unlike Pfizer, Moderna is proposing to use a half-dose of the vaccine for a booster given at least six months after the prime dose, rather than an additional full dose.
That difference may make Moderna boosters less likely to trigger side effects than the first two doses in its series.
The company presented data showing its current two-shot regimen delivers robust protection more than five months after the initial vaccination. The vaccine remained 93 percent effective in preventing all virus-related illness, and 98 percent protective against severe cases of COVID-19.
Moderna argued that the potency of its vaccine wanes over time, with neutralizing antibody levels dropping six to eight months after a second dose. FDA reviewers found that while a booster did increase antibody levels, it wasn't clear whether the protection of the initial vaccination had dropped substantially.
Moderna did not argue that its vaccine requires a booster to prevent severe disease or hospitalization. Instead, the company said one was needed to prevent infection and mild to moderate disease.
Some panel members questioned whether there was a justification for recommending boosters for people at risk because of their jobs, since there wasn't data to show higher exposure risk equated to a higher risk of severe COVID-19.
Broadly, panel members said they felt the company did not present enough robust evidence to justify a booster shot, but FDA had already set a precedent by authorizing boosters for the Pfizer vaccine.
Patrick Moore, a vaccine expert at the University of Pittsburgh, said he had "real issues" with the vote, and recommended authorization "on a gut feeling, rather than based on really, truly serious data."
"The data itself is not strong but it is certainly going in the direction that is supportive of this vote," Moore said.
The panel's vote is not binding, but the FDA is likely to follow the recommendation. A final agency decision on Moderna boosters could come within days. A Centers for Disease Control and Prevention vaccine advisory committee is expected to vote on the proposal next week.
Following the vote, panelists made it clear that while they voted in favor of boosters for the vulnerable, they were not comfortable with the possibility of widespread availability for either Pfizer or Moderna boosters— even though that was the Biden administration's initial intention.
Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, said the administration needs to define its goals. He said he's concerned officials are making the public afraid they're not protected unless they get a booster, which is not true.
“If we’re trying to prevent what is inevitable, which is a decline in neutralizing antibodies and an erosion in protection against mild or asymptomatic infection, that is a high bar to which we hold no other vaccine,” Offit said.
Peter Marks, director of FDA's vaccine division, said the agency “heard pretty loud and clearly that there was not a lot of appetite for moving down the age range very significantly, if at all.”
But he also noted that FDA has to think ahead, and there are models showing the pandemic may worsen over the winter.
"The problem here is we don't know what we don't know ... we can't simply look at what's going on with the pandemic curve and just calling it a day," Marks said.
-Updated at 4:47 p.m.