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An FDA advisory committee voted 19-2 on Tuesday to recommend use of an Omicron-specific component in a future COVID-19 vaccine booster.

"We really do need vaccines that provide broader protection against variants that have not yet emerged," said Melinda Wharton, MD, MPH, associate director of vaccine policy at the CDC, at a (VRBPAC). "Based on current evidence, if we could get broader protection with a booster that included an Omicron strain, I'm supportive of that."

But Paul Offit, MD, professor of pediatrics at Children's Hospital of Philadelphia, disagreed. "I agree we need to broaden the immune response," said Offit, who voted against adding an Omicron component. "The question is, is Omicron the right strain? I'm still not comfortable enough that we have the information we need to essentially support this new product, and I don't think it's fair to ask people to take a risk if we don't feel comfortable with the level of protection we're likely to get."

The vote capped a day-long discussion of the merits and pitfalls of various vaccines. In a released ahead of the meeting, FDA staff members noted that "The potential benefits offered by an updated vaccine containing a variant-specific component will have to be weighed against multiple uncertainties, including the future course of virus evolution, the lack of clinical efficacy data compared to earlier prototype vaccines, and potential manufacturing issues that might arise related to producing an updated vaccine formulation."

Committee members heard from Kanta Subbarao, MBBS, from the World Health Organization's Technical Advisory Group on COVID-19 Vaccine Composition, who said that her group had determined that "stand-alone data support putting in Omicron in a booster dose" for people who have already received a primary vaccine series. She noted that the Omicron variant was the most "antigenically distinct" variant of concern.

Committee members also discussed -- but did not vote on -- whether a booster vaccine should be monovalent, containing just an Omicron vaccine strain, or bivalent, containing the original vaccine strain plus an Omicron strain. Most members were in favor of a bivalent vaccine containing both the original vaccine strain plus a vaccine targeting the BA.4 or BA.5 Omicron variant, rather than another Omicron variant such as BA.1.

"I'm a fan of bivalent vaccines because the original vaccine has done so well," said Stanley Perlman, MD, PhD, professor of pediatrics at the University of Iowa. "There are multiple anecdotal and other discussions of how people are getting infected with BA.4/5 after having been infected with BA.1, so the protection of BA.1 is not so great, so that's what puts me more toward a BA.4/5-containing vaccine."

and have developed versions of their mRNA vaccines that target Omicron. And while the companies recently announced that their Omicron-containing booster shots can neutralize the BA.4 and BA.5 subvariants of Omicron, they acknowledged that it was to a lesser extent than when tested against earlier versions of the highly infectious variant.

"I'm in the bivalent camp, with an emphasis that we need to be paying attention to safety," said Bruce Gellin, MD, MPH, chief of global public health strategy at the Rockefeller Foundation in Washington, D.C. "I also want -- in the spirit of the Stanley Cup -- [to skate to] where the puck is going, rather than where it's been, so I lean to the BA.4/5 variant."

Gellin also pushed for more central planning around vaccine development. "Without such a plan, we're going to be playing whack-a-mole as this virus evolves, because it's going to continue to evolve," he said. "We'll get better at this, but we still need to get ahead of it."

VRBPAC Chair Arnold Monto, MD, emeritus professor of public health at the University of Michigan, said one issue to consider with the bivalent vaccines was that "we are going to be limited in the quantity of the Omicron components given the fact that we can't go above a certain [component] level because of the side effects, and I'm not sure we've seen direct comparisons of this in terms of antibody levels."

Several members also expressed concern about not leaving children out when it comes to a new vaccine. "How we are going to extrapolate this information for the children? We don't know,” said Jeannette Yen Lee, PhD, professor of biostatistics at the University of Arkansas for Medical Sciences in Little Rock.

"We need to think about modeling or something like that, because as we know, the youngest group just got approved a year and a half after the original approval on December of 2020," said Lee. "My concern is that if we don't have a strategy, they will always be behind in terms of the fact that the virus is evolving, and they will never be necessarily getting vaccinated against the most recent strain."

Implementing a strain composition change into practice will require FDA authorization or approval prior to deployment, FDA staff noted in the briefing document. The FDA does not have to follow the advice of its advisory committees, but typically does.

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