A Food and Drug Administration advisory committee voted unanimously (21 to 0) on Thursday to recommend updating 2023-2024 COVID-19 vaccines to a monovalent formula targeting the newest omicron subvariant lineage of XBB. Such an update would apply to both primary bursts and boosters.
The monovalent update means that subsequent COVID-19 vaccines will only target one version of pandemic coronaviruses. This is a switch from the current formula, which is bivalent and targets both the spike protein of the ancestral SARS-CoV-2 strain and the earlier leading omicron subvariants BA.4/5 (which share a spike protein ).
At Thursday’s daylong meeting, advisers reviewed data suggesting that the current bivalent vaccine continues to protect against the most serious impacts of COVID-19, but that protection against infection and hospitalization is declining over time and declining significantly faster against the XBB- variants. To date, only 17 percent of Americans have received a bivalent booster, meaning their protection has been significantly weakened since their last dose of the original vaccine formula, which only targeted the ancestral strain.
Before the update, the advisers examined data suggesting that a monovalent vaccine, rather than a bivalent one, would have a better chance of protecting against the latest Omicron subvariants and reducing the likelihood of immune responses being traced back to the ancestral strain, which no longer circulates. Since the last update of the bivalent injections, the virus has been constantly evolving, devising new ways to try to evade the immune responses built up from previous infections and vaccinations.
The FDA does not have to follow the advisory committee’s recommendations, but it almost certainly will in this case. The agency took a seemingly firm stance to treat COVID-19 the same way as the flu, with annual or biennial reviews of stem contracts and updated vaccine formulas rolled out in the fall — barring a catastrophic variant requiring urgent, off-duty scheme responses required.
Seasons and tribes
Some of the committee’s advisers — the Advisory Committee on Vaccines and Related Biological Products (VRBPAC) — again gently pushed back this plan, noting that they were not yet convinced that SARS-CoV-2 would be or has already become seasonal. Others, however, seemed more comfortable with the assumption. Committee chair Arnold Monto, professor emeritus of Epidemiology at the University of Michigan, noted that garden-variety coronaviruses that cause the common cold each year are “highly seasonal.” He said it was “premature” to suggest that SARS-CoV-2 would not fall into a seasonal pattern. Regardless of the long-term seasonality, advisors all agreed that, at least for now, an update to the vaccine formula is in order.
There was some ambiguity about which XBB subvariant to target the updated vaccines. Currently, the globally distributed XBB.1.5 is the predominant subvariant in the US, accounting for about 40 percent of US cases, according to data from the Centers for Disease Control and Prevention. But XBB.1.16, which now accounts for 18 percent of cases, is gaining ground and could be dominant in the fall. The FDA also has its eyes on XBB.2.3, which is growing in proportion and appears to be gaining ground against XBB.1.16 in India.
Preliminary data suggest that vaccines targeting the major XBB lines provide similar protection, with XBB.1.5 possibly offering a slight advantage. In discussions, the advisors did not express a strong opinion on the specific XBB lineage for the tribe, but generally supported the use of XBB.1.5. If elected, this would bring the US in line with the recommendations of advisers to the World Health Organization, which in May also recommended that countries updating vaccines move to monovalent formulas targeting the XBB lineage, with the recommendation specifically targeting XBB.1.5 emphasizes.
Peter Marks, the FDA’s chief vaccine regulator, noted at the end of the meeting that the agency will “quickly make a decision on the specific composition to recommend to manufacturers.” In terms of what the decision will be, Marks chuckled as he said, “I don’t think it will come as a surprise based on today’s discussion.” Once the FDA decides, vaccine makers (Moderna, Pfizer-BioNTech and Novavax) will work with the agency to develop and mass-produce their updated formulas, which Marks expected could be available around September.
