A group of advisers to the Food and Drug Administration on Thursday voted unanimously in favor of offering a third booster shot to many Americans who have already received two doses of Moderna's coronavirus vaccine.
In a 19-0 vote, the committee recommended a third dose be opened up to adults over 65, as well as younger people who are at high risk of contracting COVID-19 or frequently exposed to the virus because of their job — the same groups currently eligible for a booster of Pfizer's coronavirus vaccine. The third dose, which Moderna requested be half the size of the company's currently authorized dose, would be given at least six months after the second.
But panelists opposed broader use of boosters for younger, less-vulnerable Americans, citing declining infection rates in the U.S. and the unclear benefits of a third shot for those groups.
"I don't necessarily see the need for a let-it-rip campaign for boosters for everyone who's ever been vaccinated," said Michael Kurilla, one of the committee members and a division director at the National Institutes of Health.
The FDA will now weight the panelists' recommendation and make a decision on authorization. The FDA doesn't always side with its advisory committees, though it typically does.
The committee's decision followed a day of presentations from various groups, including Moderna, FDA staff and representatives from the Israel Ministry of Health, which has collected the world's most comprehensive data on booster shots.
Moderna, like Pfizer a few weeks ago, primarily relied on evidence showing a booster replenished the virus-fighting antibodies that had waned in clinical trial participants in the months following vaccination.
In a presentation to the committee, for instance, Jacqueline Miller, who runs Moderna's infection disease unit, said a half-dose booster of the company's vaccine increased neutralizing antibody levels against the dominant delta variant by 42 fold.
"This was the proof of concept that a fractional booster dose could restore neutralizing antibodies," she said.
Moderna chose to apply for authorization of a half dose in part because testing showed it could spur a similar immune response as the full dose with likely fewer side effects. A smaller dose could also expand supply by freeing up "a billion extra doses," Miller said. (Moderna has come under increasing criticism for not agreeing to supply its vaccine to more lower-income countries, or sharing its manufacturing know-how with other producers.)
Moderna, however, doesn't yet have data proving whether increasing antibody levels leads to longer lasting protection from COVID-19 or coronavirus infections. The best evidence comes from Israel, which has been rolling out boosters for months. Sharon Alroy-Preis, director of public health services for Israel's Ministry of Health, presented data showing an increase in infections over the summer — including among fully vaccinated people — that receded once boosters became more widely available.
"There is no question in my mind that the break of the curve was due to the booster dose," she said.
Israelis are mainly vaccinated with Pfizer's shot, leading some committee members to question the relevance of the evidence to Moderna's application. Both vaccines rely on similar underlying technology, and panelists ultimately supported Moderna's case.
Like Pfizer, Moderna had originally sought clearance for using boosters in anyone over 18. But the biotech changed its request after FDA panelists last month opposed general use of Pfizer's booster, and the agency issued a more narrow authorization on Sept. 22.
The FDA brought the issue up again at Moderna's meeting, calling for discussion on broader use of Moderna's booster. Though no vote was taken, panelists were largely against the idea. There is "not a lot of appetite for moving down the age range very significantly, if at all," said Peter Marks, the head of the agency's vaccine office, in summing up the panel's views.
Committee members expressed concerns about the lack of data showing a clear benefit for boosters for younger Americans. Several noted that the goal of boosting should be to maintain protection against severe disease, not necessarily mild or asymptomatic infections.
"If the goal of this vaccine is to prevent asymptomatic or mildly symptomatic infections, that is a goal for which we have set for no other vaccine," said Paul Offit, director of a vaccine center at the Children's Hospital of Philadelphia and a committee member.
The committee will reconvene on Friday to discuss booster shots for recipients of Johnson & Johnson's vaccine. Notably, they will also hear from National Institutes of Health scientists, who will present details of a study on mixing and matching booster doses, which could be of particular importance to those who had received J&J's shot.
Ben Fidler contributed reporting.