On Mar. 8, 2024, the U.S. Food and Drug Administration’s (FDA) Vaccines and Related Biological Products Advisory Committee recommended that all 2024-2025 U.S. flu vaccines be three-component (trivalent) vaccines and include an influenza A(H1N1), an A(H3N2) and a B/Victoria-lineage vaccine virus.

Because influenza B/Yamagata viruses, which are included in current four-component (quadrivalent) flu vaccines, are no longer actively circulating, their inclusion in flu vaccines is no longer warranted.