Influenza Update

From Wisconsin Division of Public Health (March 2026):

• The DHS recommends that clinicians continue administering RSV monoclonal antibody products to eligible infants until April 30, 2026.

Influenza is declining in Wisconsin, dominated by influenza B. Rates of influenza-like illnesses (ILI) in Wisconsin outpatients are low.

CDC estimates that there have been at least 28 million illnesses, 360,000 hospitalizations, and 22,000 deaths from flu so far this season. Across the U.S. there were 7,637 (12.7%) influenza detections at clinical laboratories, from the 60,262 specimens collected last week. Of detected influenza viruses at public health laboratories last week, 52.8% were influenza A and 47.2% were influenza B. Among influenza A viruses, 76.9% were H3, 23.1% were H1, and 0% were H5. CDC has reported current match estimates between circulating and vaccine strains for this season (H3: 2%; H1: 98%; B: 32%).

The percentage of primary care patients with influenza-like illness (ILI) is 3.3% and is at a moderate level. ILI activity is high in 10 states, moderate in 10 states, low in 17 states, and minimal in 13 states; Wisconsin has minimal levels. 14 additional pediatric deaths have been reported. 90 pediatric deaths due to influenza A and 25 due to influenza B have been reported for the 2025-2026 season to date; with one death in Wisconsin. Among children who were eligible for influenza vaccination and with known vaccination status, approximately 85% of reported pediatric deaths this season have occurred in children who were not fully vaccinated against influenza.

6.9% of all deaths during week 10 (Mar. 15-21) were due to pneumonia, influenza, or COVID-19, and below the seasonal epidemic threshold.

The use of rapid influenza testing is reasonable at this time based on increasing levels of circulating virus. Positive results do not need confirmation. Negative tests can be trusted as well. Use of rapid COVID-19 testing is reasonable, and positive results do not need confirmation.

• Only 33.3% of Wisconsinites have received influenza vaccine this season.
• See: https://www.dhs.wisconsin.gov/immunization/influenza.htm

• Only 12.7% of Wisconsinites have received the updated 2025/2026 COVID-19 vaccine.
  • See: https://www.dhs.wisconsin.gov/immunization/covid-19-vaccine-data.htm

https://www.cdc.gov/flu/hcp/antivirals/summary-clinicians.html

Antiviral treatment is recommended as soon as possible for any patient with suspected or confirmed influenza who:

• is hospitalized
• has severe, complicated, or progressive illness
• is at higher risk for influenza complications.

Decisions about starting antivirals for patients with suspected influenza should not wait for laboratory confirmation. Empiric antiviral treatment should be started as soon as possible in the above priority groups. Clinicians can consider early empiric antiviral treatment of non-higher-risk outpatients with suspected influenza based upon clinical judgment if treatment can be initiated within 48 hours of illness onset.

Antiviral Drug Options - supplies may be limited

• For hospitalized patients with suspected or confirmed influenza, initiation of antiviral treatment with oral or enterically administered oseltamivir is recommended as soon as possible.
• For outpatients with complications or progressive disease and suspected or confirmed influenza (e.g., pneumonia, or exacerbation of underlying chronic medical conditions), initiation of antiviral treatment with oral oseltamivir is recommended as soon as possible.
• For outpatients with suspected or confirmed uncomplicated influenza, oral oseltamivir, inhaled zanamivir, intravenous peramivir, or oral baloxavir may be used for treatment, depending upon approved age groups and contraindications.

The most common viral causes of acute respiratory infections in Wisconsin primary care practices are influenza B, seasonal coronaviruses, and RSV. For the week ending March 7, 2026, 4.1% of 13,190 specimens tested across Wisconsin and compiled by the Wisconsin State Laboratory of Hygiene were positive for SARS-CoV-2. The most commonly identified gastopathogen is norovirus.

Over the past 4 weeks the typical ARI case has been 39.8 years old; 78% of patients have been female. 24% of patients identified a sick contact 1-3 days before illness onset and they typically present to the clinic 5.4 days after illness onset. 33% of illnesses are characterized as mild, with 67% having moderate symptoms and 0% having severe symptoms.

*estimate based on WSLH statewide data

** estimate based on primary care patients seen at five clinics and 1 urgent care in Dane County

*** includes HKU1, NL63, 229E and OC43