Wisconsin is currently dealing with elevated respiratory virus activity, with influenza B leading the way as the most frequently identified virus in laboratory testing. Hospitalizations are up, particularly among children ages 0 to 4. Norovirus has also been spreading through schools statewide, and RSV activity remains at a moderate level.
Influenza B Is the Dominant Strain
Influenza B is the virus showing up most often in Wisconsin lab results right now, and its activity is still climbing. This is a notable shift from the typical pattern where influenza A dominates early in flu season and influenza B picks up later. Hospitalizations are elevated across the state, with young children bearing a disproportionate share of severe cases.
Influenza B tends to hit children and young adults harder than influenza A in some seasons. Symptoms are the same as any flu: sudden fever, body aches, chills, fatigue, cough, and sore throat. Most people recover within one to two weeks, but the very young, the elderly, and people with chronic health conditions face higher risks of complications like pneumonia.
Wisconsin’s flu vaccination rates have been declining for four consecutive seasons after peaking during the pandemic in 2020-2021. Only 26% of children ages 5 to 17 received a flu shot during the 2024-2025 season, and just 24% of adults ages 18 to 49 did. Coverage was highest among seniors at 64%, and among children under 5 at 43%. Those low uptake numbers in school-age kids and working-age adults help explain why flu is spreading so effectively.
RSV Remains Moderate but Worth Watching
RSV activity in Wisconsin is classified as moderate by the CDC, and nationally about 9% of RSV tests are coming back positive. RSV is most dangerous for infants, toddlers, and adults over 65. In babies and very young children, it can cause bronchiolitis, an inflammation of the small airways in the lungs that leads to wheezing and difficulty breathing. In healthy older children and adults, RSV typically looks like a bad cold: runny nose, cough, low fever, and fatigue.
The overlap of RSV with influenza B is part of what’s driving the elevated hospitalization numbers in children under 5. If your child is breathing rapidly, making a whistling sound when exhaling, or struggling to drink fluids, those are signs the illness has moved beyond a typical cold.
Norovirus Is Hitting Schools Hard
Norovirus outbreaks have been impacting Wisconsin schools significantly enough that the state Department of Public Instruction created a dedicated resource page for school nurses and administrators. Norovirus causes the sudden-onset vomiting and diarrhea that people commonly call “stomach flu,” though it has nothing to do with influenza. It spreads incredibly easily through contaminated surfaces, food, and direct contact with sick individuals.
Symptoms come on fast, usually 12 to 48 hours after exposure, and include nausea, projectile vomiting, watery diarrhea, and stomach cramps. Most people feel terrible for one to three days and then recover fully. The biggest risk is dehydration, especially in young children and older adults. You’re most contagious while symptomatic and for the first two days after symptoms stop, so keeping kids home from school during that window is important for slowing spread.
Norovirus is notoriously hard to kill. Alcohol-based hand sanitizers don’t work well against it. Washing hands with soap and water for at least 20 seconds is the most effective prevention. Contaminated surfaces need to be cleaned with a bleach-based solution rather than standard household cleaners.
Other Viruses in the Mix
Beyond the big three, adenoviruses and rhinoviruses are circulating as they do year-round. Rhinoviruses cause about half of all common colds, and most infections stay mild: runny nose, sneezing, sore throat. Adenoviruses can produce a wider range of symptoms including fever, bronchitis, sore throat, and pink eye. These viruses rarely cause serious illness in healthy adults, but they add to the general wave of sickness that makes it feel like everyone around you is coughing.
Tick Season Is Approaching
While respiratory viruses dominate the picture right now, Wisconsin residents should also be aware that tick-borne illness season is on the horizon. Wisconsin is one of the highest-risk states in the country for Lyme disease, with most cases occurring in June and July. Ticks become active whenever temperatures stay above freezing, so early spring hikes and yard work can bring exposure even before summer. If you’re spending time outdoors as the weather warms, checking for ticks after coming inside and wearing long pants in wooded or grassy areas reduces your risk substantially.
How to Tell What You Have
With so many viruses circulating simultaneously, it can be hard to figure out what hit you. A few patterns help sort things out:
- Flu (influenza B): Comes on suddenly with fever, body aches, and exhaustion. Cough and sore throat are common, but vomiting and diarrhea are not typical in adults.
- RSV: Looks like a heavy cold with lots of nasal congestion and cough. In adults it’s usually mild. In infants and toddlers, watch for labored breathing and poor feeding.
- Norovirus: Vomiting and diarrhea are the hallmarks, often with little to no respiratory symptoms. Onset is abrupt and the illness is short, usually resolving within three days.
- Common cold (rhinovirus/adenovirus): Gradual onset, mostly upper respiratory symptoms like a runny nose and sneezing. Fever is uncommon in adults.
If you’re unsure whether you have the flu or something else, rapid tests at pharmacies and clinics can identify influenza and COVID-19 within minutes. Knowing which virus you have matters most for people at higher risk of complications, since antiviral treatment for flu works best when started within 48 hours of symptom onset.