Originally published by our sister publication Infectious Disease Special Edition
By Marie Rosenthal, MS
The FDA recommended the virus strains to be used in the 2025-2026 influenza vaccines after reviewing U.S. and global surveillance data.
Trivalent seasonal influenza vaccines include two influenza A subtype viruses (H1N1 and H3N2) and one influenza type B virus. Influenza virus strains were selected based on the influenza vaccine production method: egg-based, cell-based or recombinant.
As a result of the meeting with the federal partners, the FDA recommends that the trivalent formulation of egg-based influenza vaccines for the 2025-2026 U.S. influenza season will contain the following:
- A/Victoria/4897/2022 (H1N1)pdm09–like virus;
- A/Croatia/10136RV/2023 (H3N2)–like virus; and
- B/Austria/1359417/2021 (B/Victoria lineage)–like virus.
The FDA recommends that the trivalent formulation of cell-based or recombinant influenza vaccines for the 2025-2026 U.S. influenza season contain the following:
- A/Wisconsin/67/2022 (H1N1)pdm09–like virus;
- A/District of Columbia/27/2023 (H3N2)–like virus; and
- B/Austria/1359417/2021 (B/Victoria lineage)–like virus.
These recommendations are in line with what the WHO recommended.
A Different Process
The FDA recommendation was made without the input from outside experts who are usually part of the equation. Typically, the FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) also weighs in before the decision is made. However, VRBPAC was canceled the day before the meeting was to be held.
Instead, the FDA convened a closed meeting of scientific and public health experts from the FDA, CDC and Department of Defense, where they evaluated and analyzed U.S. and global surveillance data related to the epidemiology and antigenic characteristics of flu viruses currently circulating.
When this meeting were not held, there was concern among infectious disease specialists, particularly those whose expertise is vaccinology, that not holding these meetings would delay the recommendation and not give vaccine manufacturers enough time to develop the vaccines.
However, with the decision this week, the FDA does not anticipate any impact on the timing or availability of vaccines for the American public.
“Well, clearly the process this year was not the ‘usual order’,” said William Schaffner, MD, a professor of preventive medicine and health policy at Vanderbilt University School of Medicine, in Nashville, Tenn. “However it is apparent that a clear decision has been made with consultation of many interested parties, and this should allay the concern that I've heard about the availability of influenza vaccines this coming fall in a timely manner. This selection of strains ought to assure that we do have influenza vaccines available when we need them this fall.”
In fact, Sanofi, which makes Fluzone, FluBlok and FluZone High-Dose for seniors, said it accepted the recommendation and has begun manufacturing. Sanofi plans to begin shipping flu vaccines this summer “so that health systems, hospitals, pharmacies, physician practices, nursing homes and other facilities can begin administering vaccines at the onset of the next flu season,” the company said in a release.
Dr. Schaffner continued: “If there is a downside, and frankly, I think it’s a small downside concerning not having a formal meeting of VRBPAC, it’s that there isn’t the opportunity for the external experts to participate in the discussion or an opportunity for public comment.
“That said, if you look back at the history of these decisions, U.S. personnel have participated in the WHO discussions, and there’s always been concurrence with the WHO selection.”
Because the United States had not yet left the WHO, they were part of the discussions for the WHO recommendations, which are the same as the FDA’s, although the American attendance was virtual rather than in person.
Among declining vaccination rates, the United States is experiencing one of the worst flu seasons in decades, and rates of flu-related hospitalizations were at a 15-year high. According to estimates by the CDC, there have been 40 million illnesses, 520,000 hospitalizations and 22,000 deaths from the flu through the week ending March 1. Twenty children died from influenza the week ending March 8, bringing the pediatric mortality to 134 children.
“The U.S. is weathering one of its most severe flu seasons in decades, underscoring the need to protect people against seasonal influenza infection. As the world leader in flu vaccines, Sanofi works relentlessly to ensure we are prepared, which is why our manufacturing does not miss a beat as we provide eligible Americans with a portfolio of immunizations to help protect against flu infection and the potentially serious complications it can cause," said Thomas Grenier, MSc, MBA, the head of Vaccines, North America, at Sanofi.
The 2024-2025 influenza season has peaked, according to the CDC. However, flu-related medical visits, hospitalizations and deaths remain elevated, and the CDC expects several more weeks of flu activity. Twenty-five jurisdictions surveyed by the CDC are still seeing high or very high activity as of the week ending March 8.
The predominant viruses throughout the country are influenza A(H1N1)pdm09 and A(H3N2), the CDC said. For the week ending March 8, positive samples for influenza were 16.1%, people seeking healthcare for a respiratory illness was 4.3% and deaths attributed to influenza was 1.9%—all down from the week before.
Influenza vaccination is recommended for all people 6 months of age and older without contraindications (https://www.cdc.gov/flu/hcp/acip/index.html).
