Credit ACIP/CDC
#17,939
Twelve years ago this week (see Two B's Or Not Two B's? That Is the Question) the FDA approved the use of a quadrivalent seasonal flu vaccine that would incorporate both influenza B virus lineages (B/Victoria and B/Yamagata).
Up until that time, a trivalent formulation, containing two A strains and 1 B strain, had been the standard for seasonal influenza vaccines.
One of the surprises coming out of our COVID pandemic was the suppression of influenza for the first few years, and the apparent extinction of the B/Yamagata lineage. It has now been 48 months since the last reported human infection.
As a result, the decision was made last fall to remove the B/Yamagata strain from the flu vaccine, and to return to a trivalent shot, as soon as possible.
Use of Trivalent Influenza Vaccines for the 2024-2025 U.S. Influenza Season
FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) met on March 5, 2024, to discuss and make recommendations on the selection of influenza viruses for the composition of influenza vaccines for the 2024-2025 U.S. influenza season. This follows the October 5, 2023, VRBPAC meeting during which FDA and the committee engaged in scientific discussion pertaining to the continued need for a quadrivalent formulation of seasonal influenza vaccine for the U.S. as there have been no confirmed detections of circulating B/Yamagata lineage viruses worldwide after March 2020.
Influenza B viruses are classified into two lineages: B/Yamagata and B/Victoria. However, the evidence indicates that the B/Yamagata lineage virus no longer poses a public health threat. During the October 2023 meeting, the committee unanimously voted to recommend excluding the B/Yamagata lineage component from quadrivalent seasonal influenza vaccines as soon as possible.
In the interest of public health, FDA strongly recommended to influenza vaccine manufacturers the removal of the B/Yamagata lineage virus from seasonal influenza vaccines in the U.S. for the 2024-2025 influenza season. FDA and the manufacturers have been working together so that the move from quadrivalent to trivalent seasonal influenza vaccines occurs for the upcoming influenza season.
2024-2025 Trivalent Seasonal Influenza Vaccines for the United States
Influenza virus strains for a trivalent vaccine composition for use in the U.S. were recommended on March 5, 2024, by the Committee based on the influenza vaccine production method: egg-based and cell- or recombinant-based. Trivalent seasonal influenza vaccines include two influenza A viruses (H1N1 and H3N2) and one influenza B virus.
During this meeting, the advisory committee reviewed and evaluated the surveillance data related to epidemiology and antigenic characteristics of recent influenza isolates, serological responses to 2023-2024 vaccines, and the availability of candidate strains and reagents.
The committee recommended that the trivalent formulation of egg-based influenza vaccines for the U.S. 2024-2025 influenza season contain the following:
The committee recommended that the trivalent formulation of cell- or recombinant-based influenza vaccines for the U.S. 2024-2025 influenza season contain the following:
- an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
- an A/Thailand/8/2022 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Use of FDA-Approved Quadrivalent Seasonal Influenza Vaccine Outside of the United States for 2024-2025
- an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
- an A/Massachusetts/18/2022 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Of note, not all countries will be able to revert to trivalent seasonal influenza vaccines as quickly as FDA has facilitated the process for the United States. For those manufacturers who have an existing FDA-approved quadrivalent seasonal influenza vaccine and want to export that quadrivalent vaccine for use outside the United States, the committee also recommended the inclusion of a second B strain, a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus for quadrivalent egg-, cell- or recombinant-based vaccines.
Next Steps
Based on the scientific evidence, and since the October 2023 VRBPAC meeting, FDA has been planning for the use of trivalent seasonal influenza vaccines for the U.S. for the 2024-2025 influenza season. As such, FDA has been engaging and interacting with manufacturers of FDA-approved seasonal influenza vaccines and providing scientific and regulatory advice to them to facilitate the timely availability of approved safe and effective trivalent seasonal influenza vaccines for the 2024-2025 U.S. influenza season. FDA anticipates that there will be an adequate and diverse supply of approved trivalent seasonal influenza vaccines for the United States in the coming season.
