With an eye toward enhancing protection against the coronavirus, which is still evolving and circulating, federal health advisers said Thursday that the next round of COVID-19 vaccines should be updated to target the now-dominant XBB strains.
The unanimous recommendation from the U.S. Food and Drug Administration’s vaccine advisory committee follows that of agency staff, who in a memo acknowledged that while older vaccine formulas can still help stave off severe disease, “protection wanes with time and is reduced against subsequent waves of variant viruses.”
Data suggest using the latest dominant coronavirus strain that more closely matches current circulating oomicron sublineages “is warranted for the 2023-2024 vaccination campaign,” FDA staff added.
“I think that we need a better vaccine. We should be updating it, and I think it’s pretty straightforward,” said Dr. Eric Rubin, a committee member and infectious disease expert at the Harvard T.H. Chan School of Public Health.
The committee’s recommendation will be reviewed by the FDA. The U.S. Centers for Disease Control and Prevention also is expected to weigh in on the matter, with its Advisory Committee on Immunization Practices scheduled to discuss COVID-19 vaccines on June 23.
Virtually all versions of the coronavirus currently circulating in the U.S. are descendants of the original oomicron variant that walloped the nation in late 2021 and early 2022. But among those, the XBB family — which includes XBB.1.5 and XBB.1.16, unofficially dubbed “Kraken” and “Arcturus,” respectively — is dominant almost to the point of monopoly.
According to the most recent estimates from the CDC, XBB sublineages comprise nearly 99% of circulating coronavirus in the U.S, displacing the BA.5 subvariant that dominated the nation for much of last year.
Evidence is accumulating that “suggest that a vaccine composition that more closely matches circulating virus strains can significantly improve vaccine-induced immunogenicity and protection,” FDA staff said.
“It’s a great idea to base the vaccine on what’s circulating right now,” UC San Francisco infectious diseases expert Dr. Peter Chin-Hong said in an interview. “And XBB is the main game in town. It’s been around for some time now. It probably will continue to be dominant.”
Given recent patterns over the last year, the coronavirus has been evolving more incrementally, Chin-Hong said. So he said picking a vaccine formula based on a current dominant subvariant is likely to still be helpful heading into the fall and winter, when some officials and experts expect a degree of resurgence.
The updated vaccine, the FDA panel agreed, should be a “monovalent” shot focused on XBB rather than the “bivalent” booster unveiled in September 2022, which protected against both the then-dominant omicron subvariants and the ancestral coronavirus strain.
Future iterations of the vaccines need not protect against the ancestral strain, scientists say. A World Health Organization technical advisory group said in May there is no longer a need for that since the original version of the coronavirus that emerged in late 2019 in Wuhan, China, is essentially extinct.
In the U.S., XBB.1.5 made up the majority of circulating virus in the early spring but now is estimated to comprise about 40% of specimens, CDC figures show. The upstart XBB.1.16 is gaining ground and is now estimated to make up 18% of cases nationwide.
In Los Angeles County, XBB.1.5 accounted for 66% of analyzed specimens as of early May.
Though this past winter saw nowhere near the same degree of devastation as the pandemic’s first two winters, the nation and California still saw an uptick in coronavirus-positive hospitalizations, as well as a considerable number of deaths. From October through early June, about 75,000 COVID-19 deaths have been reported nationally. That’s more than double the average annual number of flu deaths in the decade preceding the COVID-19 pandemic.
There’s emerging consensus regarding the value of periodically updating COVID-19 vaccines.
“In order to improve protection, in particular against symptomatic disease, new formulations of COVID-19 vaccines should aim to induce antibody responses that neutralize XBB descendant lineages,” the WHO advisory group said.
And it’s possible the vaccines will need to be reformulated again, depending on how the coronavirus continues to evolve.
“This is not going to be the final formulation for this vaccine for evermore,” FDA vaccine chief Dr. Peter Marks said. “It will probably require another update at some point.”
In terms of figuring out a near-term vaccine formulation, however, the WHO advisory group noted XBB.1.16 has very small genetic and antigenic differences from XBB.1.5. “The spike antigens of both of these lineages are genetically and antigenically very closely related, with only two amino acid differences between” them.
Updating the vaccination formula ahead of last autumn and winter season was helpful, officials said.
“Observational data indicated that [last year’s updated] COVID-19 vaccines provided improved protection from COVID-19 caused by sublineages of omicron, including the BA.4/BA.5 sublineage, compared to the original vaccines,” FDA staff said in their statement.
