Advisers to the Food and Drug Administration decided in a unanimous 19-0 vote Thursday to endorse Moderna COVID-19 booster shots for the most vulnerable to severe complications despite some concerns about the depth of evidence, acknowledging that the urgency of the pandemic required prompt action.

The Vaccines and Related Biological Products Advisory Committee recommended a third Moderna shot for people who are 65 years old or older, adults with underlying health conditions that put them at higher risk for severe COVID-19 and adults at high risk of exposure because they work in an essential job or live in an institution like a prison or homeless shelter.

The panel suggested giving half the dose of the first two, given at least six months after the second shot.

The next step is for the FDA to formally issue an emergency use authorization. The agency usually follows its advisers’ recommendations. After that, the Centers for Disease Control and Prevention will undergo a similar process. Its advisers will likely endorse or refine the FDA’s decision in its own recommendations, and CDC Director Rochelle Walensky has a final say.

The FDA advisory panel met for nearly seven hours to parse data Moderna submitted to the FDA. Moderna found a booster shot ramped up antibodies without serious side effects.

Questions about data

Many of the panel members criticized the data the drugmaker presented, while endorsing the need to be as proactive as possible when it comes to people at risk of severe disease.

“The data are not perfect, but these are extraordinary times,” said Eric Rubin, a member of the committee and chair of the Harvard University department of immunology.

The challenges with the data included that one of the presentations to the committee concerned data from Israel, which used Pfizer booster shots.

Moderna’s trial was relatively small, testing 171 people who received a third dose after receiving the standard two doses. The company also collected data from another 173 people who received half of the standard dose for their first two shots, but interpreting that information could be challenging.

The deputy director of vaccine applications at FDA’s Center for Biologics Evaluation and Research, Doran Fink, confirmed during the committee meeting that the agency’s primary focus was on the 171 people who received the authorized dose.

The company also barely missed one of its two primary endpoints, or barometers of success, in showing efficacy in its clinical trial.

About 87.9 percent of people getting a booster saw at least a four-fold rise in neutralizing antibodies, while 98.4 percent of people saw a four-fold rise after a two-dose primary series. Moderna hoped the difference would be less than 10 percent.

“It’s a fairly limited group and only meets one of the pre-specified criteria for emergency use,” said Jeannette Lee, professor of biostatistics at the University of Arkansas for Medical Sciences.

There were concerns that Moderna did not provide enough evidence of waning immunity for severe disease and death, a concern that also impacted a similar vote on Pfizer boosters last month. On Sept. 17, the VRBPAC endorsed a third Pfizer shot for the same populations after voting down a request by the drugmaker to approve them for all adults. The committee’s scientists found there wasn’t enough evidence that immunity was waning for most people.

Top FDA officials at the meetings stressed that even mild infections may lead to long COVID-19 symptoms, but the committee was not presented with data to support that point.

Another sticking point for the committee was whether people at high risk of exposure through their jobs or an institution like a prison or shelter are at higher risk of severe COVID-19. The idea that people at greater risk of exposure also face higher risk of severe complications from COVID-19 shapes the emergency use authorization Moderna is seeking.

The recommendation to include essential workers and people in institutions was abruptly supported by the committee during last month’s vote on Pfizer boosters in the frenzied few minutes after the committee voted down boosters for a broader group.

“It’s so important that these recommendations are evidence-based,” said Cody Meissner, a Tufts Medical Center professor of pediatrics. “If we can’t defend these recommendations based on evidence, it’s going to further complicate getting this vaccine into every single adult American. And that’s really what we want to do.”

James Hildreth, president of Meharry Medical College, pushed back on attempts to exclude essential workers, citing the pandemic’s deeper impact on communities of color in large part because they did not have the luxury of working from home.

The committee is not permitted to consider questions of global supply in its deliberations, but Rubin did stress the importance of first vaccinations over boosters, including in other countries without the United States’ ample access to vaccine.

Even after endorsing the shots, some panelists scolded Moderna for not submitting more complete information. One panelist said the pace of its collection of safety data has been “sluggish.”

“It’s very important for companies that are coming to VRBPAC as we consider an EUA that they take seriously the idea that we need to see good, solid data,” said Patrick Moore, a professor at the University of Pittsburgh Cancer Virology Program.