FDA Advisory Committee Unanimous: COVID-19 Vaccines Should be Monovalent, Contain XBB Strain

The FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) unanimously voted 2023-2024 COVID-19 vaccines should be updated to a monovalent XBB strain.

On Thursday, June 15, the US Food and Drug Administration’s (FDA) Vaccines and Related Biological Products Advisory Committee (VRBPAC) met in an open session to discuss and make recommendations on the strains to be included in updated COVID-19 vaccines for the 2023-2024 vaccination campaign.

Just after 4 pm, VRBPAC voted on the following question: “For the 2023-2024 Formula of COVID-19 vaccines in the US, does the committee recommend an update of the current vaccine composition to a monovalent XBB-lineage?”

After all 21 VRBPAC members voted “Yes,” the committee moved on to their primary discussion topic: “Based on the evidence and other considerations presented, please discuss selection of a specific XBB lineage (eg, XBB.1.5 or XBB.1.16 or XBB.2.3) for inclusion in the 2023-2024 Formula of COVID-19 vaccines in the US.”

Over the course of a day-long meeting, the Center for Biologics Evaluation and Research (CBER) committee viewed and responded to presentations from the FDA, US Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), Moderna, Pfizer, and Novavax, and heard opinions from speakers during an open public forum.

VRBPAC had previously voted to move toward a unified strain composition for COVID-19 primary and booster vaccines, on January 26, 2023. By simplifying strain composition, the committee aimed to provide more transparent information to the public and health care providers. Additionally, the COVID-19 virus has evolved so significantly that there is no longer a need to include the original, wild-type Wuhan strain in the next generation of vaccines.

By the spring of 2023, virus surveillance revealed the XBB sublineages were the predominant COVID-19 strains, both in the US and the world. The XBB parent lineage is a recombinant of BA.2.10.1 and BA.2.75 sublineages, indicating that we may expect more recombination variants in the future. Recombination occurs during virus replication when a cell is infected by more than 1 variant.

By June 2023, XBB sublineages accounted for more than 95% of the world’s circulating COVID-19 variants. “The current trajectory of virus evolution indicates that XBB will likely be the progenitor of SARS-CoV-2 variants in the near future,” the FDA wrote in a briefing document. “XBB descendent lineages are highly immune evasive. To improve protection, particularly against symptomatic disease, COVID-19 vaccines should induce antibodies that neutralize XBB descendent lineage viruses.”

The director of the FDA Office of Vaccines Research and Review, David Kaslow, MD, reiterated this during the meeting. “First, we need a periodic update. Second, it’s time to move from the current bivalent to a monovalent.” He noted we may shift to a bivalent strain composition in the future, but that current evidence suggests the need for a monovalent COVID-19 vaccine of the XBB lineage.

The FDA will take VRBPAC’s recommendation into serious consideration before relaying their official 2023-2024 COVID-19 vaccine composition guidelines to vaccine manufacturers.

Selection of Strain(s) to be Included in the Periodic Updated COVID-19 Vaccines for the 2023-2024 Vaccination Campaign. FDA Briefing Document Vaccines and Related Biological Products Advisory Committee Meeting June 15, 2023. Accessed June 15, 2023.

US Food and Drug Administration. Vaccines and Related Biological Products Advisory Committee June 15, 2023 Meeting Announcement. Accessed June 15, 2023.