
Following an advisory group discussion last week on COVID-19 vaccine updates for the fall, the Food and Drug Administration (FDA) on Jun 16 asked manufacturers to develop monovalent (single-strain) vaccines that target the Omicron XBB.1.5 subvariant.
The announcement followed a unanimous vote from the FDA Vaccines and Related Biological Products Advisory Committee (VRBPAC) to switch to a monovalent vaccine for the fall. After hearing data from federal experts and the vaccine companies, VRBPAC members expressed a preference for the XBB.1.5 subvariant.
Novavax last week said its XBB.1.5 candidate prompts a functional immune response against XBB.1.5, XBB.1.16, and XBB.2.3 subvariants, suggesting that its adjuvanted protein-based vaccine may be useful against drifted subvariants. In the United States, XBB.1.5 is most common, but the proportion is declining as newer XBB subvariant levels rise.
The FDA said in an addendum to its strain selection announcement that although the XBB sublineages continue to evolve, the spike protein sequences of XBB.1.5, XBB.1.16, and XBB.2.3 are similar, with few amino acid differences.
In its presentation to VRBPAC last week, a representative from Pfizer said the company could begin distributing doses of an XBB.1.5 monovalent vaccine by the end of July, but it would take a month longer to start distributing an XBB.1.16 vaccine. Any other formulation would have an October distribution schedule.