South Dakota enters the 2025–2026 influenza season after several recent winters marked by elevated flu activity, according to the South Dakota Department of Health.
State health officials say influenza remains a persistent threat for older adults, young children, and people with chronic medical conditions, particularly in rural areas where access to care can be limited.
Why H3N2 Matters
Federal health officials are closely watching influenza A(H3N2), a subtype that has historically been associated with more severe seasons. A newly identified version of the virus, known as H3N2 subclade K, began appearing in global surveillance after the 2025–2026 vaccine formula was finalized.
Researchers have identified multiple mutations in the virus’s hemagglutinin protein. CDC surveillance shows the new subclade now accounts for nearly 90% of H3N2 viruses characterized in the United States.
Impact on Older Adults and Rural Communities
CDC medical officers say seasons dominated by H3N2 tend to result in higher hospitalization and death rates among adults 65 and older and young children. South Dakota’s older population and long travel distances to hospitals can amplify those risks during a heavy flu season.
Vaccination and Treatment
Health officials continue to recommend annual flu vaccination, even when the circulating virus differs from the vaccine strain. Early national data suggest vaccination reduces the risk of severe illness and emergency care, particularly in children. The CDC and FDA report no evidence that the current H3N2 subclade is resistant to approved antiviral medications, which can be used alongside vaccination for people at higher risk.
What to Watch
The South Dakota Department of Health updates influenza activity through its online dashboard during flu season. Officials encourage residents to stay home when sick, practice good respiratory hygiene, and seek medical care promptly if symptoms worsen.
Sources
South Dakota Department of Health – Influenza Dashboard
South Dakota Department of Health – Vital Statistics Reports
Centers for Disease Control and Prevention – FluView Weekly Report
Journal of the American Medical Association Medical News, Dec. 19, 2025
