U.S. Facing Severe Flu Surge Driven by H3N2 Subclade K
A dominant H3N2 subclade K is driving an unusually severe U.S. flu season, straining hospitals, increasing pediatric cases, and highlighting vaccine and national policy challenges.
Overview
Flu cases have surged across the U.S., with H3N2 subclade K causing most infections; over 11 million illnesses, 120,000 hospitalizations, and 5,000 deaths reported this season.
Hospitals near capacity in many regions; clinicians report rising severe illness in children, including pneumonia and neurological complications, especially among unvaccinated pediatric patients.
This season's vaccine was selected before subclade K emerged; although imperfect at preventing infection, vaccines still reduce severe disease, hospitalizations, and deaths, especially in children.
Recent HHS changes and public comments questioning flu vaccination, plus cuts to mRNA research funding, could hinder vaccine uptake and future rapid-response development.
Experts advise vaccination, early antiviral treatment, RSV monoclonal antibodies for infants, masking, hand hygiene, and staying home when sick to limit transmission and severe outcomes.
Analysis
Analysis unavailable for this viewpoint.
Sources (3)
FAQ
H3N2 subclade K is a newly emerged genetic subgroup of the seasonal influenza A(H3N2) virus that has accumulated several mutations in its hemagglutinin gene, making it antigenically drifted from earlier H3N2 strains and the current vaccine strain, which has contributed to rapid spread and higher overall case numbers this season.[4][5] H3N2 seasons are historically linked with more hospitalizations and severe outcomes, especially in older adults and other high‑risk groups, so a fast-growing new subclade can more easily strain hospitals and increase severe disease.
Early estimates from surveillance studies indicate that the current flu vaccine still provides meaningful protection against subclade K, reducing medically attended influenza by about 32–39% in adults and 72–75% in children and adolescents, even though the virus emerged after vaccine strain selection and is antigenically drifted.[3][5] This means the vaccine is less than perfect at preventing infection but remains important for lowering the risk of severe illness, hospitalization, and death, particularly in children.[3]
Pediatric cases have risen sharply in this H3N2-dominant season because children often have less prior immunity to influenza A(H3N2) and tend to experience higher infection rates during intense flu waves, leading to more hospitalizations.[3][4] H3N2, including subclade K, can cause complications such as pneumonia, neurologic symptoms, and in rare cases organ failure, with severe disease disproportionately affecting unvaccinated children and those with underlying conditions.
Experts recommend getting vaccinated against flu, using early antiviral treatment (such as oseltamivir) for high‑risk or severely ill patients, giving RSV monoclonal antibodies to eligible infants, wearing masks in crowded indoor spaces, practicing hand hygiene, and staying home when sick to limit spread and protect hospitals and vulnerable groups.[3][4] Health agencies also stress standard infection‑prevention measures in healthcare settings, including appropriate personal protective equipment when caring for influenza patients.[4]
Recent shifts in U.S. health policy, including public discussion that questions flu vaccination and reductions in support for mRNA and other rapid‑response vaccine research, risk lowering vaccine uptake now and could slow the development and deployment of more adaptable influenza vaccines in future seasons.[3][5] Since H3N2 subclade K emerged after vaccine strain selection, experts argue that sustained investment in flexible vaccine platforms is important to respond more quickly to similar antigenic drift events.
History
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