What "the flu shot is 40% effective" actually measures
Three surveillance networks put 2025/26 effectiveness between 22% and 45% against a drifted H3N2 virus. The figure is a comparison between vaccinated and unvaccinated people who all got tested.
Next season's flu vaccines are being rebuilt around the H3N2 variant from August
WHO updated all three components for the 2026-2027 northern hemisphere season after subclade K dominated globally, and recommended a new candidate vaccine virus for an H9N2 avian strain.
A presidential memo asks why the US schedule covers more diseases than peer countries
The 5 December directive tells HHS and the CDC to compare the American childhood schedule with those of other wealthy nations, using a count of diseases as its benchmark.