Influenza Vaccine Availability, Effectiveness, Formulations 2025
Influenza vaccines, known as flu shots, protect people against influenza viruses each flu season, say the U.S. Centers for Disease Control and Prevention (CDC), the European Medicines Agency (EMA), and the World Health Organization (WHO). As of March 16, 2025, the WHO says that influenza vaccines do not cause seasonal flu since they are made with either killed or weakened viruses. In the United States, influenza vaccines are manufactured differently (cell, egg) and have various levels of effectiveness.
U.S. FDA Influenza Vaccine Formulations 2024-2025-2026
On March 13, 2025, the U.S. Food and Drug Administration (FDA) recommended vaccine manufacturers for the virus strains used in influenza (flu) vaccines for the 2025-2026 U.S. flu season. These recommendations are similar to the previous year's strain selection. With today's action, the FDA does not anticipate any impact on the availability of flu shots for the American public. The FDA followed the WHO's recommendations announced on February 28, 2025.
The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) met on March 5, 2024, and finalized the quadrivalent and trivalent influenza vaccine options for the 2024-2025 flu season. The trivalent vaccines for use in the 2024-2025 northern hemisphere influenza season contain the following: Egg-based vaccines - 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. Cell culture- or recombinant-based vaccines: 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. For quadrivalent egg- or cell culture-based or recombinant vaccines for use in the 2024-2025 northern hemisphere influenza season, the WHO recommends the inclusion of the following as the B/Yamagata lineage component: a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
U.S. CDC Influenza Vaccine Recommendations 2024-2025
On August 29, 2024, the U.S. Centers for Disease Control and Prevention (CDC) published updates (73(5);1–25) on the 2023–24 recommendations of the Advisory Committee on Immunization Practices (ACIP) concerning the use of seasonal influenza vaccines in the United States (MMWR Recomm Rep 2022;72[No. RR-2]:1–24). The ACIP meeting in June 2024 included presentations led by Lisa Grohskopf, Jill Ferdinands, and Lenee Blanton Influenza Division, CDC/NCIRD - Influenza Updates, Work Group Considerations, and Proposed Recommendations for the 2024-25 Influenza Season. The Influenza Work Group leader, Dr. Jamie Loehr, led the presentations. As of August 2024, the CDC says all flu vaccines for the 2024-2025 season will be trivalent, and most will be thimerosal-free or thimerosal-reduced vaccine (91%), and about 21% of flu vaccines will be egg-free.
Flu Shots Administered and Availability
The CDC's Weekly Influenza Vaccination Dashboard reported that, as of 2025, over 92 million flu shots had been distributed in the U.S., targeting the 2024-2025 flu season. About 158 million flu vaccines were distributed during the 2023-2024 flu season, 173 million during 2022-2023, and 194 million during 2021-2022.
As of February 28, 2025, the percentage of the population reporting receipt of an influenza vaccine is 45.8% (44.6-47.0) for children and 45.2% (44.4-46.1) for adults 18+, including 70% (68.1-71.8) among adults 65+. The CDC reported on May 25, 2024, that about 48% of U.S. adults received a flu shot during 2023-2024.
Influenza Vaccine Effectiveness
The CDC's ACIP reviewed Influenza Vaccine Effectiveness (VE) interim data from the 2023-2024 flu season on October 23, 2024. The CDC published vaccine effectiveness (VE) data during the 2009-2023 flu seasons. Anthony C. Fries, Ph.D., with the U.S. DOD, presented 'Influenza Surveillance and Mid-Season VE at the U.S. FDA Vaccines and Related Biological Products Advisory Committee meeting on March 5, 2024. The DoD calculated the Beneficiary VE for the 2023-2024 Mid-Season Influenza Estimates, which ranged from 43% to 53%. A meta-analysis of flu vaccine VE studies conducted from 2017 through 2022 and published in the journal Vaccines on February 28, 2024, shows the real-world effectiveness of seasonal influenza vaccination averaged 41.4%. The flu shot VE varied substantially by virus type and age group.
Flu Shot Immune Imprinting
The concept of "immune imprinting" originated with investigating immune responses to infection by divergent strains of influenza viruses. Scientists found that people had more robust neutralizing antibody responses toward influenza strains that they had been exposed to during childhood. Mechanistically, when different strains of a pathogen infect the host cell, the immune system dedicates most of the response toward recalling the immune effectors used for the original exposure instead of generating reactions against the new strains, thus resulting in immune evasion.
