This story has been updated.
The 19 members of the FDA’s Vaccines and Related Biological Products Advisory Committee voted to authorize a 50-milligram dose — half the dose used in the primary series of shots — to boost immunity against COVID-19 at least 6 months after the second dose. Those who might need a booster are the same groups who’ve gotten a green light for third Pfizer doses. They include people:
- Over age 65
- Ages 18 to 64 who are at higher risk for severe COVID
- Who are at higher risk of catching COVID because they live in group settings like nursing homes or prisons, or because they are frequently exposed at work, as health care workers are
The agency is not bound by the committee’s vote but usually follows its recommendations.
Some members of the committee said they weren’t satisfied with the data Moderna submitted to support its application but, for practical reasons, said it wouldn’t be fair to take booster doses off the table for Moderna recipients when Pfizer’s boosters were already available.
“The data are not perfect, but these are extraordinary times and we have to work with data that are not perfect,” said Eric Rubin, MD, editor-in-chief of TheNew England Journal of Medicine and a temporary voting member on the committee.
Patrick Moore, MD, a professor at the University of Pittsburgh Cancer Institute who is also a temporary voting member, said he voted to approve the Moderna boosters based “more on a gut feeling than on truly serious data.”
“I’ve got some real issues with this vote,” he said.
“We need to see good solid data, and it needs to be explained well,” Moore said, challenging companies making future applications to do better.
Next, the FDA will have to formally sign off on the emergency use authorization, which it is expected to do. Then, the CDC’s Advisory Committee on Immunization Practices will meet to make formal recommendations on use of the Moderna boosters. That group is scheduled to meet next Thursday to take up questions of exactly how these boosters should be used.
Peter Marks, MD, head of the FDA’s Center for Biologics Evaluation and Research, cautioned that the CDC is more constrained in making recommendations under an emergency use authorization than it would be if the boosters had gotten full approval. So it will likely align its vote with the conditions of the emergency use authorization from the FDA.
After the advisory committee votes, the director of the CDC has to approve its recommendation.
Overall, data shows that two doses of the Moderna vaccine remains highly effective at preventing hospitalization and death. But over time, levels of the body’s first line of defense against a virus — its neutralizing antibodies — fall somewhat. This drop seems to correspond with an increased risk for breakthrough cases of COVID-19.
Data presented by Moderna today showed the risk of breakthrough infections increased by 36% in study participants who received the vaccine in their clinical trials, compared to people in the same study who received a placebo first, and got the vaccine later, when the trial was unblended. Their protection was more recent, and they had fewer breakthrough infections.
In considering booster doses, the FDA has asked drugmakers to do studies that look at the immune responses of small groups of study participants and compare them to the immune responses seen in study participants after their first two vaccine doses.
To be considered effective, boosters have to clear two bars. The first looks at the concentration of antibodies generated in the blood of boosted study volunteers. The second looks at how many boosted study participants saw a four-fold increase in their blood antibody levels a month after the booster minus the number of people who saw the same increase after their original two doses.
Moderna presented data that its boosters met the first criteria, but failed to meet the second, perhaps because so many people in the study had good responses after their first two doses of the vaccines.
The FDA’s advisory committee will reconvene Friday to hear evidence supporting the emergency use authorization of a booster dose of the Johnson & Johnson vaccine.