The article evaluates the efficacy of the 2025–2026 season influenza vaccine against an H3N2 subclade K variant that circulates widely and has key hemagglutinin substitutions. The vaccine induces antibodies that effectively recognize this variant in almost 40% of vaccinated persons. These antibodies are considered regulatory to be likely protective against H3N2 subclade K infections. The H3N2 subclade K variant is antigenically advanced from the vaccine strain, but the difference in human sera is not as great as in ferret experiments. The results do not differ significantly according to the age of the volunteers. The vaccine thus probably partially prevents the disease caused by this virus.[1][3]