South Dakota health officials are urging residents to get flu vaccinations as national health experts warn of a potentially difficult flu season, coming on the heels of what health officials called the state’s most severe season in 15 years.
Why it matters
The U.S. flu season is just beginning to ramp up, but international trends suggest trouble ahead, according to epidemiologists at Your Local Epidemiologist, a public health newsletter. The United Kingdom, Japan, and Canada are already experiencing steep increases in flu cases driven by a mutated strain of influenza A (H3N2) that evolved over the summer, according to the newsletter.
The mutation occurred after this year’s flu vaccines were formulated in February, meaning the vaccines will recognize some, but not all, of the updated virus, epidemiologists say. Despite this mismatch, vaccination remains highly effective. U.K. health data shows flu vaccines reduce hospitalization by 70-75% in children and 30-40% in older adults, according to Your Local Epidemiologist.
The mutated H3N2 strain already accounts for 51% of flu samples in the United States, according to the Centers for Disease Control and Prevention. While influenza-like illness remains below epidemic thresholds nationally, cases are beginning to climb, particularly in Louisiana and Southern states, according to CDC data.
Impact on South Dakotans
For South Dakota, the warning comes at a critical time. The state experienced its worst flu season in over a decade during 2024-2025, with 20,266 laboratory-confirmed cases and 43 deaths, according to the South Dakota Department of Health dashboard. That case count marked the highest in the past 10 years, according to department data.
Flu vaccination rates in South Dakota have declined for three consecutive years, according to department statistics. The state recorded 234,770 flu vaccinations during the 2024-2025 season, down 17% from a recent high of 283,318 during the 2021-22 season, according to department data.
Dr. Joshua Clayton, state epidemiologist for the South Dakota Department of Health, has emphasized the importance of preventive measures. “Influenza can be a very serious illness,” Clayton said. “Taking preventative measures like regularly washing hands, covering your cough, and getting vaccinated if you choose against the flu will protect you and your family.”
South Dakota averages 33 flu deaths annually, according to Clayton. Last season exceeded that figure, according to department data. The state reported its first flu death of the 2024-2025 season in a Corson County resident over age 65, according to the department.
Declining vaccination rates
Declining vaccination rates contributed to increased hospitalizations and more severe cases during the last flu season, health officials said. The 2024-2025 flu vaccine was roughly 50% effective at preventing hospitalizations, according to health officials.
Flu vaccines still provide protection against other circulating strains and can reduce the severity of illness even when vaccine-virus mismatch occurs, according to public health experts.
The CDC recommends South Dakotans take several preventive steps: get the flu vaccine, wash hands regularly, cover coughs and sneezes, and seek early treatment if flu symptoms develop. Antiviral medications like Tamiflu can reduce illness duration if started early, according to the CDC.
Flu tests can still detect the new H3N2 strain, allowing for prompt treatment, according to health officials.
The South Dakota Department of Health maintains an online flu dashboard tracking weekly case counts, hospitalizations, and deaths throughout the flu season.
