The 2025 flu season has begun, and the new flu vaccine was released in the United States in September. Influenza viruses are unique in their ability to mutate or change, so every year the flu vaccine needs to be updated in response. This year the early news is good: the vaccine appears to be an unusually close match to this year’s flu strains.
This optimistic take is drawn from results in Southern Hemisphere countries that experience winter months before the U.S. and give us an early signal about what to expect. This year, the match between the flu strains that were the basis for the vaccine and the flu viruses that actually circulated was ~98%. That’s about as close a match as we can get.
A strong match is one of many components that determine how well the flu vaccine will work, and unfortunately there are many real-world factors that work against it. In a well-matched year, overall vaccine effectiveness usually ranges from 50% to 60% for preventing medical visits and hospitalizations, and this is what we are seeing so far.
Because it’s so early in the season, it’s helpful to look back to past U.S. flu seasons that began with similar conditions to gauge what to expect. The 2022-23 and 2023-24 seasons had a similar match, and a vaccine effectiveness rate of roughly 50%. In contrast, the 2017-18 season had much lower vaccine effectiveness – about 10% – and clinical outcomes were devastating. Deaths and hospitalizations reached 50,000 and 1 million, respectively, nearly double the rates seen in years with a good match.
Even in a year with a great match, vaccines don’t completely prevent flu, but they do blunt its severity. The evidence so far suggests that with good uptake of this year’s flu shot we should expect fewer hospitalizations and fewer deaths – especially among those at highest risk – older adults, infants and children younger than 5 years of age, pregnant women, and people with chronic illnesses. That could be tens of thousands of lives saved thanks to this vaccine.
A question likely to surface is whether the vaccines offered this year contain thimerosal, a mercury-based additive used in some forms of the flu shot. In July 2025, Health and Human Services Secretary Robert F. Kennedy, Jr. announced that beginning with the 2026-27 flu season that all vaccines were expected to be thimerosal-free.
Even before this directive, most forms of the flu shot given in the U.S. did not contain thimerosal, and that remains true this year as well. However, there are some settings – mostly public health clinics and workplace vaccine programs – which use multi-dose vials that may still contain thimerosal. Patients who prefer a thimerosal-free flu shot may need to ask for it in advance and schedule an alternative option accordingly.
Requirements for childhood vaccines differ depending on their role in community vs individual protection. At present, no states require the flu vaccine for K-12 school attendance, but there are a few places – such as Connecticut, Rhode Island, and New York City – that mandate it for children attending daycare or preschool programs. Regardless of mandates, most private insurance plans, Medicaid, and Medicare include flu vaccination as a covered preventative service.
The flu vaccine reminds us that not all vaccines serve the same purpose. Some provide a larger community health benefit, protecting the public as a whole; others primarily protect individuals, while others land somewhere in the middle. All are worthwhile goals, but recognizing the difference allows us to promote them more thoughtfully.
Public health officials have done a good job of right-sizing flu vaccine messaging, emphasizing benefits without overselling them, and trusting people to make their own informed decisions. The fact that flu vaccination is voluntary and yet widely adopted shows that trust and honest communication can be as effective as mandates.
Monique Yohanan, MD, MPH, is a senior fellow at Independent Women, a physician executive and healthcare innovation leader, and a former advisor for Adia Health.
The views and opinions expressed in this commentary are those of the author and do not reflect the official position of the Daily Caller News Foundation.
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