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Twice each year international influenza experts meet to discuss recent developments in human and animal influenza viruses around the world, and to decide on the composition of the next influenza season’s flu vaccine. Due to the time it takes to manufacture and distribute a vaccine, decisions on which strains to include must be made six months in advance.
Which means the composition of the northern hemisphere’s vaccine must be decided upon in February of each year, while decisions on the southern hemisphere’ vaccine are made in September.Today the WHO released their recommendations for the composition of this fall's 2025-2026 Northern Hemisphere flu vaccine, which updates the H3N2 virus for both egg and cell-based vaccines. First, the press release from the WHO, after which I'll have a bit more.
Recommendations announced for influenza vaccine composition for the 2025-2026 northern hemisphere influenza season
28 February 2025
News release
Reading time: Less than a minute (229 words)
The World Health Organization (WHO) today announced the recommendations for the viral composition of influenza vaccines for the 2025-2026 influenza season in the northern hemisphere. The announcement was made at an information session at the end of a 4-day meeting on the Composition of Influenza Virus Vaccines, a meeting that is held twice annually.
WHO organizes these consultations with an advisory group of experts gathered from WHO Collaborating Centres and WHO Essential Regulatory Laboratories to analyse influenza virus surveillance data generated by the WHO Global Influenza Surveillance and Response System (GISRS). The recommendations issued are used by the national vaccine regulatory agencies and pharmaceutical companies to develop, produce, and license influenza vaccines for the following influenza season.
The periodic update of viruses contained in influenza vaccines is necessary for the vaccines to be effective due to the constant evolving nature of influenza viruses, including those circulating and infecting humans.
The WHO recommends that trivalent vaccines for use in the 2025-2026 northern hemisphere influenza season contain the following:
Egg-based vaccines
- an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
- an A/Croatia/10136RV/2023 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Cell culture-, recombinant protein- or nucleic acid-based vaccines
The recommendation for the B/Yamagata lineage component of quadrivalent influenza vaccines remains unchanged from previous recommendations: a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
- an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
- an A/District of Columbia/27/2023 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Normally within a week or two of the release of the WHO vaccine recommendations, the FDA's advisory group ACIP (Advisory Committee on Immunization Practices) meets to recommend the formulation for the U.S. fall flu vaccines. The three-day ACIP meeting scheduled for late this week has already been postponed (see notice below).
Last night Chris Dall at CIDRAP reported that the upcoming ACIP meeting on the flu vaccine - scheduled for March 13th - has also been cancelled.
FDA cancels advisory committee meeting on flu vaccine strain selection
Chris Dall, MA
February 27, 2025
An upcoming meeting of a Food and Drug Administration (FDA) vaccine advisory board to select virus strains for next season's flu shot has been canceled.
The March 13 meeting of the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) was scheduled to make recommendations for the flu strains that will be included in the 2025-26 flu shot or nasal spray for the Northern Hemisphere. VRPBAC typically meets in March to make those recommendations, which are based on what flu strains are expected to be circulating in the fall and winter. The FDA uses the recommendations to direct vaccine manufacturers on the composition of the shots, which take roughly 6 months to produce.
VRBPAC members were alerted that the meeting was canceled in an email from the FDA that did not include an explanation, according to the Washington Post. The cancelation is raising concerns that the timing and availability of next season's flu shot could be affected.
While a delay of a few weeks - or even a month or more - might not be enough to disrupt vaccine deliveries this fall, there isn't a lot of slack in the timetable. And the manufacturing of (mostly egg-based) vaccines can sometimes face unexpected delays, particularly when a new strain is introduced.
While the numbers vary from year-to-year, 6 weeks ago the :
CDC estimates that during the 2023-2024 season, flu vaccination prevented 9.8 million flu-related illnesses, 4.8 million medical visits, 120,000 hospitalizations, and 7,900 deaths.
And that was during a much less-severe flu season that we are seeing this year. Add in the potential for increased H5N1 activity in the months ahead, and reducing seasonal flu - and potential reassortment opportunities - should be a priority.
Whether that translates into action, remains to be seen.
