Every flu season, the question comes up, “Is the vaccine actually helping this year?” This year according to the CDC flu MMWR, the answer is yes, even with a drifted strain, and the details matter.
What the Data ShowAcross U.S. surveillance networks this season:
In children:
These are meaningful reductions, particularly in hospitalization, which is where the biggest impact is for pediatric patients.
The Strain MismatchMost of the circulating viruses this season have been influenza A(H3N2) subclade K, which is antigenically different from the strain used in the vaccine. That mismatch matters. It lowers overall vaccine effectiveness and explains why we are still seeing a lot of flu. However, vaccination is still reducing the likelihood of needing care and the likelihood of hospitalization. That’s consistent with what we would expect biologically, partial immune recognition still translates into less severe disease.
The Bigger Issue: UptakeAs of February 22, 2026, fewer than half of children and adults in the U.S. have received a flu vaccine this season. So while it’s easy to focus on the circulating virus mismatch, the larger issue is that many patients remain unvaccinated. In the Emergency Department, we should continue to recommend vaccination. Even late in the season, there is benefit as long as influenza is circulating.
We should also use antivirals appropriately. While the reduction in symptom duration, roughly a day, may not be clinically meaningful for many otherwise healthy children, there are groups where treatment matters because of higher risk for complications. In those patients, oseltamivir should be part of routine management. Specifically:
The Bottom LineThis is not a perfectly matched vaccine year, but the vaccine is still reducing visits and hospitalizations, especially in children. The dominant circulating strain, A(H3N2) subclade K, has drifted, but protection against severe outcomes remains. Vaccination rates remain suboptimal, and improving uptake likely has more impact than any incremental change in strain match.
ReferenceMaloney P, Reeves EL, Wielgosz K, et al. Interim Estimates of 2025–26 Seasonal Influenza Vaccine Effectiveness — United States, September 2025–February 2026. MMWR Morb Mortal Wkly Rep 2026;75:116–123. DOI: http://dx.doi.org/10.15585/mmwr.mm7509a2.
Note: This post was edited with the assistance of artificial intelligence (ChatGPT, OpenAI GPT-5.3). The content, interpretation, and final wording were reviewed and approved by the author. And, oh yeah, AI also helped make the banner image because I’m not that good at drawing.