June 15, 2023 – A panel of advisers to the FDA unanimously agreed today that the next COVID-19 vaccines should target the XBB variants of the SARS-CoV-2 virus now in circulation in the United States, but questioned whether the population as a whole needs booster shots and how often they should be given.
The Vaccines and Related Biological Products Advisory Committee of the FDA voted 21-0 in favor of the recommendation about the strain to be used in the next crop of vaccines.
In the briefing document for the meeting, FDA staff said the available evidence suggests that a monovalent (single-strain) XBB-lineage vaccine “is warranted” for the 2023-2024 vaccination campaign and would replace the current bivalent vaccine, which targets the original version of the virus and two strains from the Omicron variant.
FDA staff also noted how such a shift would be in line with the World Health Organization toward targeting the XBB family of subvariants. European regulators have done this as well.
The FDA is not obligated to act on the panel’s recommendations. But the agency often does and is highly likely to do so in this case. Vaccine companies will need the recommendation from the FDA to begin making vaccines for the fall.
New Shot Every Year?
The FDA asked its expert panel to vote only on the question about the makeup of future vaccines in terms of which strain to include.
But panelists also raised other questions during the meeting, including concerns about moves toward tying COVID vaccinations into the model of annual flu shots.
Paul Offit, MD, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, argued for greater focus on the response of T cells after vaccination, even in light of the already recognized waning of antibody protection.
In a recent Substack article, Offit called T cells the “unsung hero” of the pandemic. They take longer to develop after infection or vaccination than the antibodies that first attack the virus, but immune memory cells called B and T cells “are long-lived,” and their “protection against severe disease often lasts for years and sometimes decades.”
Offit said he was concerned about using a blanket approach for future recommendations for COVID vaccinations, following the one now in place for influenza vaccines. The CDC recommends flu shots for everyone 6 months and older, with rare exceptions.
“We need to continue to define who those high-risk groups are and not make this a recommendation for everybody every season,” he said.
Offit offered his own experience as an example. While he had been vaccinated against the virus’s early Wuhan strain, he still was infected, most likely with a variant that emerged later.
“That was a drifted virus. That’s why I had a mild infection but I didn’t have a severe infection, because presumably I had T cells which prevented that severe infection, which may last for years,” Offit said.
Pfizer and Moderna, the two companies that make mRNA-based COVID vaccines, are working on experimental products meant to protect against both flu and SARS-COv-2 in one shot. Novavax, maker of a more traditional protein-based COVID shot, is doing the same.
The idea of these combination products is to make it more convenient for people to protect against both viruses, while also offering companies some marketing advantages.
But without referring to these drugmakers’ plans for future combo flu-COVID shots, members of the FDA panel on Thursday raised objections to an assumption of routine annual vaccines against variants of SARS- CoV-2.
Among the panelists who expressed concerns was Henry H. Bernstein, DO, a former member of the CDC’s Advisory Committee on Immunization Practices.
Bernstein questioned the approach of dubbing these the “2023-2024 formulas,” as this approach conveyed a sense of an expectation for a need for annual vaccines, as happens with flu.
“It’s not clear to me that this is a seasonal virus yet,” said Bernstein, who is also a professor of pediatrics at Zucker School of Medicine at Hofstra/Northwell in New York.
In response to Bernstein’s point, Arnold Monto, MD, the acting chair of today’s FDA panel suggested such a pattern could emerge, while also agreeing that it’s too soon to say for sure.
A professor emeritus at the University of Michigan, Monto’s career included pandemic planning and emergency response to virus outbreaks, including the 1968 Hong Kong influenza pandemic, avian influenza, and the original SARS.
“I think it’s premature to say that this virus will not become seasonal,” Monto said about SARS-CoV-2. “I agree. We’re not there yet, but we may be.”
At the end of the meeting, Monto recapped the meeting’s key points, noting that there was a general consensus that the XBB.1.5 subvariant would be the best to use in future COVID shots.
He also noted that Novavax, which makes the more traditional protein-based vaccine, along with Pfizer and Moderna, already have honed in on this subvariant, which would allow for rapid development of updated COVID vaccines.
“The fact that most of the manufacturers are ready to work on an XBB 1.5 [vaccine] is an added reason to select this strain or this variant, given the immunologic data,” Monto said.
Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, said the demands involved in manufacturing vaccines tilts toward annual changes.
“Practically, we’re going to have one update per year, barring a heroic effort to deal with a strain that pops up that is essentially so different that it requires us to mobilize tremendous resources to address that strain change,” he said.
Marks questioned the panelists’ concerns about likening flu and COVID vaccination practices. The FDA staff’s intent was to try to help the public understand the need for follow-on vaccination, he said.
“I’m really having trouble understanding that committee’s need to bristle against something that’s similar to influenza. People understand a yearly influenza vaccine,” Marks said.
And it’s not certain when another major change in the COVID virus will follow the XBB subvariant, but it’s likely one will — and soon, Marks said.
“It looks like probably by next fall, there’ll be further drift from this,” he said.
Informing the Public
Marks also stressed the need to better convey the benefits of vaccination to people in the US.
CDC data estimate that 70% of the US population completed an initial series of the original monovalent vaccines, with only 17% then getting bivalent shots. There’s even a decline among people ages 65 and older. CDC estimates 94% of this group completed their primary series, but only 43% got the bivalent booster dose.
“We have to do better because we have not done a good job today communicating to the American public what’s going on here,” Marks said.
Researchers also are still trying to determine the best timing for people to get additional COVID shots. Finding the “sweet spot” where people can maximize additional protection is tricky, with people most protected if they happen to get shot near the beginning of an uptick in viral spread, the CDC’s Ruth Link-Gelles, PhD, MPH, told the panel during a presentation.
“You’re going to get the best incremental benefit if it’s been longer since your last vaccine,” she said. “But of course, if you wait too long since your last vaccine, you’re left with very little protection, and so you’re at higher risk of severe illness.”
Like FDA’s Marks, Link-Gelles stressed the need for persuading more people to get follow-on vaccines.
“Most Americans, at this point, haven’t even received the bivalent and so are a year or more out from their monovalent dose and so have relatively little protection left,” she said.