The unanimous vote by the FDA’s independent advisory panel marks the emergence of global consensus that the vaccine should be restarted to no longer include the original strain from the early days of the pandemic.
The available version of the vaccine is bivalent, meaning it targets both the original strain and the newer BA.4 and BA.5 omicron variants. But in the four years since the coronavirus began spreading in humans, it has continued to develop new ways to circumvent existing immunity.
The newly chosen target, XBB, is a recombinant virus – a mixture of two descendants of the BA.2 omicron variant. Several flavors of XBB circulate in the US today, but the committee and the FDA seemed to favor the use of XBB.1.5, a highly transferable version of the virus on which vaccine manufacturers have already conducted significant testing.
Because XBB’s spinoffs are so similar, the hope is that a new shot based on one version will provide a breadth of cross-protection against whatever virus is circulating this fall, even if it’s not an exact match.
“Obviously the data suggests that the old variants are no longer circulating. XBB is. So yes, [a change] makes sense,” said Adam C. Berger, director of the Division of Clinical and Health Research Policy in the Office of Science Policy at the National Institutes of Health.
Executives from Moderna, Pfizer and Novavax, the vaccine companies that provide shots in the US, presented data from animal and some limited human tests for various updated candidates. The potential timeline for distribution of the shots varies depending on the strain selected by the FDA, with companies able to provide XBB.1.5 vaccines earlier than other options.
Updating the vaccine this year was an easy decision for committee members. Still, some debated whether the scientific understanding of the virus is settled enough to predict that the shot will be updated annually, similar to how the flu vaccine is updated each year. Viral evolution is inherently unpredictable, and the seasonal pattern of this virus is still emerging.
Calling it the 2023-2024 coronavirus vaccine “suggests that this will be once a year, and I’m not sure we’re personally there with this virus — that it’s not necessarily seasonal,” said Henry Bernstein, professor of pediatrics at Zucker School of Medicine at Hofstra/Northwell in New York.
Those uncertainties must be balanced against the need for a plan that will allow companies to produce adequate doses, and allow public health officials to clearly communicate when people need to get their shots, said Peter Marks, director of the Center for Biologics Evaluation and Research. at the FDA.
“We certainly agree that covid-19 is not the flu, but from a public health point of view where you have to make tens upon tens of millions of vaccine doses, get them deployed and get them into people’s arms … it reduces to a similar kind of campaign ,” Marks said.
A major concern may prove to be uptake of the vaccine. Only 1 in 5 adults have received a bivalent booster, according to data from the Centers for Disease Control and Prevention.
That worries public health experts because, although immunity to vaccinations and infections continues to protect most people from serious illness and death, protection clearly wanes over time. Data presented at the meeting showed that protection against hospitalization drops significantly four to six months after a bivalent booster. Older adults are most vulnerable.
“Barring some exceptional development of a resistant virus … I think we have a chance this fall to weaponize vaccines,” Marks said.
Researchers are working on a number of next-generation vaccines that may be more variant-proof, long-lasting or able to shut down transmission of disease. But in the short term, the most practical option is to track the virus and continue to update the vaccine as it evolves — an uncertain pursuit that several committee members said was unsatisfactory, if necessary.
“We have to be prepared that this is going to be an ongoing process,” said Jerry Weir, director of the Division of Viral Products in the FDA’s Center for Biologics Evaluation and Research.