Health experts and officials have battled over the idea of authorizing booster vaccine doses, as data has shown that vaccine protection against infection has waned over the last few months, thoguh most people remain heavily protected against severe COVID. The U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) voted in late September to authorize an additional dose of the Pfizer shot for certain high-risk groups who had gotten their second dose at least six months prior. But Moderna and Johnson&Johnson recipients have had to wait, as the vaccine manufacturers submitted their applications for booster authorization later than Pfizer, delaying FDA meetings over the two vaccines' submission to mid-October. Now, an FDA committee has finally made its recommendation on Moderna boosters.
On Oct. 14, the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) voted to recommend a booster shot of the Moderna vaccine for certain vaccine recipients who received their second dose at least six months prior, per The New York Times. In a unanimous vote of 19 to 0, the panel chose to endorse an additional shot of this vaccine for the same groups of people eligible for a Pfizer booster: those 65 years and older, and those 18-64 who are at high risk of severe COVID for medical, institutional, or occupational reasons.
Unlike the third Pfizer shot, however, Moderna's booster is a half-dose of its primary series. The vaccine manufacturer asked the FDA to authorize booster shots of 50 micrograms, which is half of the 100-microgram dose Moderna recipients received for their first two shots.
Moderna and Pfizer also faced notable differences in their data. As Eric Rubin, PhD, an adjunct professor of immunology and infectious diseases at the Harvard T. H. Chan School of Public Health, explained to the NYT, Pfizer had real-world data from Israel, where millions of people have already received an additional dose of the Pfizer vaccine as part of Israel's booster campaign. Moderna, on the other hand, does not have real-world, large scale data, so it is only "presenting the results of a relatively small trial," Rubin explained.
Recent research has shown more favorable results for Moderna's original two-dose series than for Pfizer's. According to a Sept. 24 study from the CDC, the Moderna vaccine has stayed the most protective in preventing COVID hospitalization from March to August at 93 percent, while Pfizer was just 88 percent effective in the same timeframe. The study also found that Pfizer's vaccine dropped in efficacy after four months to 77 percent, while Moderna's held steady.
In its argument to the FDA committee, Moderna said that its boosters helped prevent infection and mild to moderate disease. The manufacturer presented data showing that the mean antibody level of participants in its study was 1.8 times higher after the booster dose than it was after the second shot, meeting FDA criteria, per the NYT. But its data failed to meet another requirement, as the booster dose only raised neutralizing antibodies four-fold in 87.9 percent of people. The agency required a boost in at least 88.4 percent of participants—but the panel still decided to vote in favor of Moderna boosters.
"I just want to explain why I voted yes; it is more gut feeling rather than based on really truly serious data," panel member Patrick Moore, a professor at the University of Pittsburgh Cancer Institute, said, per Politico. "The data itself is not strong, but it is certainly going in a direction that is supportive of [boosters]."
The FDA does not technically have to follow the panel's recommendations, but it is expected to do so. According to the NYT, the agency typically makes its final determination on authorization within a few days of the advisory committee's meeting. After the VRBPAC voted in favor of the Pfizer vaccine, the FDA announced its authorization five days later.
Many virus experts say it is unlikely that the FDA will choose not to authorize the Moderna booster following the VRBPAC's endorsement, as it has already set a precedent by authorizing additional Pfizer shots. "From a pragmatic point of view, because we've already approved it for Pfizer, I don't see how we can possibly not approve it for Moderna," Stanley Perlman, MD, a professor microbiology and immunology at the University of Iowa, told the NYT.
Once the FDA gives its determination, the CDC's Advisory Committee on Immunization Practices (ACIP) will have to meet to discuss and choose what groups to endorse Moderna boosters for before the agency's director, Rochelle Walensky, MD, issues the CDC's final determination on the additional shots. The ACIP is already scheduled to meet on Oct. 20 and Oct. 21 to discuss boosters.