Flu Vaccine Isn’t a Perfect Match – But It Still Protects Kids from Severe Illness

Influenza A(H3N2) subclade K has emerged as the predominant circulating strain during the 2025-26 flu season. While the current influenza vaccine is an imperfect match for this strain, available data continue to show meaningful protection against severe disease, especially in children and adolescents.

Recent early-season data from England found that influenza vaccination reduced flu-related emergency department visits and hospital admissions by 72–75% among children and adolescents under 18 years. In adults, vaccine effectiveness was lower, estimated at 32–39%, underscoring the particularly strong benefit of vaccination in pediatric populations.

These findings reinforce an important message for pediatric primary care teams: even in seasons with strain mismatch, influenza vaccination remains the most effective tool for preventing severe illness, hospitalization and complications in children.

Providers are encouraged to continue recommending influenza vaccination for all eligible patients and to counsel families that while vaccination may not fully prevent infection, it significantly reduces the risk of severe outcomes.