A Food and Drug Administration advisory panel voted Thursday to recommend Moderna booster shots for emergency use authorization, bringing millions of Americans one step closer to being eligible for an additional dose.
The panel, called the Vaccine and Related Biological Products Advisory Committee, voted unanimously in favor of authorizing the shots. The decision will now go to the FDA, which is expected to make a final ruling in the coming days.
The panel’s recommendations for the Moderna booster followed the blueprint it established last month for booster shots of Pfizer-BioNTech’s vaccine: It would be authorized for adults ages 65 and up; people in long-term care facilities; people with underlying medical conditions; and people at high risk of exposure to the coronavirus because of their job. These individuals would be eligible at least six months after their second shot.
Moderna’s booster dose would be given as a half dose of 50 micrograms, compared to the original 100 micrograms given in the initial vaccination series. (By contrast, Pfizer’s booster is the same 30 microgram dosage as its initial series.)
Jacqueline Miller, therapeutic area head for infectious diseases at Moderna, said in her presentation to the committee that the company chose the half dose because it wanted to use the lowest dose possible needed to induce an immune response.
Miller noted that using a lower-dose booster has worked well for other vaccines, including the DTaP vaccine, which protects against tetanus, diphtheria and whooping cough.
The meeting was less contentious than the group’s discussion last month on Pfizer, when the advisors rejected authorizing Pfizer boosters for all adults 18 and up six months after their initial vaccinations and instead opted to limit the eligibility.
Data shows that protection from Moderna’s vaccine has waned: People who were vaccinated earlier in the year were more likely to have a breakthrough infection compared to people who received their vaccinations several months later, Miller said. Nearly all of these breakthrough infections were caused by the delta variant.
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Several of the breakthrough cases were considered severe, and there were two deaths.
"We are concerned about the breakthrough disease that we’ve been observing in the participants in the (original clinical trial), and particularly the breakthrough cases that we’re starting to see in severe disease in the older adults," Miller said.
The booster dose led to higher antibody levels, including antibodies against the delta variant.
Still, a handful of breakthrough infections — 20 cases — were reported among people who received a booster.
Dr. Doran Fink, a deputy director of the FDA’s division of vaccines, noted that it’s still unknown what levels of antibodies are needed for protection.
Both Moderna’s presentation and the FDA’s analysis found the booster to be safe, though several committee members noted they wanted to see more safety data from the company.
Side effects from the booster were similar to those seen after the second dose. Those include arm pain, fatigue, headache and muscle aches.
However, the booster trial didn’t include enough participants to evaluate whether the extra dose raised the risk for myocarditis, Fink said.
Myocarditis, or inflammation of the heart muscle, has been linked to both Moderna and Pfizer’s COVID-19 vaccines. The condition is rare and mostly commonly seen in men under 30.
Hui-Lee Wong, associate director for innovation in the FDA’s Office of Biostatistics and Epidemiology, noted that myocarditis occurred in similar rates following the second doses of both Pfizer and Moderna.
In data from Israel, where 3.7 million people have received a Pfizer booster shot, 17 cases of myocarditis were reported, said Dr. Sharon Alroy-Preis, director of public health services for Israel’s Ministry of Health, who presented Thursday.
"The rate of it is really, really low compared to what you would have expected, if it was the same rate as after the second dose," she said. "Perhaps it’s because we’re giving this dose five months or later" as opposed to giving two doses three weeks apart.
The same group of advisers will convene Friday to discuss a booster shot of Johnson & Johnson’s COVID-19 vaccine. It will also review the results of a National Institutes of Health study on "mixing and matching" COVID-19 vaccines. That study found that giving people who initially received the Johnson & Johnson vaccination a booster dose of either Pfizer or Moderna led to a stronger immune response than a second Johnson & Johnson dose.
Next week, a group of advisers to the Centers for Disease Control and Prevention will take up the question of who should receive the Moderna and Johnson & Johnson booster shots. If the boosters are recommended, CDC Director Dr. Rochelle Walensky would then sign off and shots can start going into arms.
This story was originally published on NBC News.