Flu Cases Surge Across the U.S. as New H3N2 Strain Spreads
Flu Cases Are Surging Across the United States in 2026 Flu Surge in the U.S. — Key Summary Points Flu activity has reached record-high levels across the United States this season. 8% of all medical visits were flu-related in the week ending December 27 — the highest since 1997. 120,000 hospitalizations and 5,000 deaths have been reported so far this flu season. Hospitalizations increased 48% week-over-week, signaling rapid spread. Flu test positivity jumped to 33% nationwide, up from 9% in early December. Several states, including Colorado, Utah, and Wyoming, reported positivity rates above 45%. The CDC classified flu activity as “high” nationwide and “very high” in parts of the Northeast. New York City shows slight declines, but flu levels remain very high. Michigan is experiencing a severe early surge, with pediatric ICUs treating critically ill children. A mutated Influenza A (H3N2) strain known as subclade K is driving infections. Over 90% of tested U.S. flu cases are linked to H3N2, with most identified as subclade K. Current flu vaccines may be less targeted against subclade K but still reduce severe illness. Wastewater data shows a 146% increase in flu virus concentration nationwide. Flu infections are rising in 17 states, stable in 7, and declining in 24. Common symptoms include fever, cough, fatigue, runny nose, and body aches. Health officials stress that vaccination remains the best protection, especially for children. Childhood flu vaccination rates have declined, raising public health concerns. Experts warn flu season can last until May, and it’s not too late to get vaccinated. Handwashing, staying home when sick, and mask use can help limit spread. Flu Cases Surge Across the U.S. as New H3N2 Strain Spreads Flu activity is surging across the United States this winter, reaching levels not seen in decades. New data from the Centers for Disease Control and Prevention (CDC) shows record-high medical visits, rising hospitalizations, and growing concern among health experts as a mutated flu strain spreads nationwide. Flu Activity Reaches Historic Highs Nationwide For the first time since flu tracking began in 1997, 8% of all medical visits during the week ending December 27 were related to influenza or flu-like illness, according to the CDC. Key national highlights: 120,000 hospitalizations so far this season 5,000 flu-related deaths 48% week-over-week increase in hospital admissions Flu activity classified as “high” nationwide This marks one of the most intense early flu seasons in recent history. Flu Test Positivity Rates Climb Rapidly CDC surveillance data shows a sharp rise in flu positivity since December: 33% of flu tests were positive nationwide (23,350 out of 70,757 tests) Early December positivity was just 9% Some states exceeded 45% positivity States With Highest Positivity Rates Colorado Montana North Dakota South Dakota Utah Wyoming Northeast Reports “Very High” Flu Activity The CDC categorized flu levels as “very high” in parts of the Northeast, including: New York Massachusetts North Carolina Health officials caution that despite some localized declines, the virus remains widespread. Wastewater Data Confirms Rapid Flu Spread Wastewater surveillance from WasteWaterSCAN, a Stanford-led tracking system, reinforces CDC findings: 146% increase in flu virus concentration between early and late December Indicates broader community spread, including untested or asymptomatic cases CDC Projections: Where Flu Is Rising or Falling As of December 30: Flu cases rising in 17 states Stable or unreported in 7 states Declining or likely declining in 24 states Health officials warn trends can reverse quickly. What Is the New Flu Strain Driving This Surge? A newly dominant mutation known as subclade K is accelerating the spread. What Is Subclade K? A mutation of Influenza A (H3N2) Structurally different from previous H3N2 strains More effective at evading existing immunity CDC data shows: 91% of tested U.S. flu cases were H3N2 90.5% of those were subclade K Is the Flu Vaccine Still Effective? While the 2025–2026 flu vaccine is less targeted against subclade K, experts stress it still provides important protection. According to early international data: Hospitalization rates are similar to last season Vaccination reduces severity and complications Vaccine effectiveness remains meaningful Health authorities emphasize that vaccination still prevents severe illness and death. Common Flu Symptoms This Season Symptoms linked to H3N2 and subclade K include: Fever Cough Runny nose Fatigue Muscle aches and chills Children, older adults, and immunocompromised individuals remain at highest risk. New York City: Slight Decline, But Risk Remains High New York City health officials report early signs of decline, but warn the flu remains widespread. Key NYC data: 128,000+ flu cases this season Higher than the past two years 6% drop in childhood flu vaccinations Health Commissioner Dr. Michelle Morse warned: “We’re not out of the woods yet.” Officials stressed that flu season can last until May. Michigan Flu Surge: Pediatric Cases Raise Alarm Michigan is experiencing a severe and early flu season. Michigan Highlights: 2,110 flu-related hospitalizations 306 children under age 4 hospitalized 40% increase in hospitalizations compared to last year Pediatric ICUs reporting children on ventilators Children accounted for 69% of emergency visits for respiratory viruses during Christmas week. Doctors emphasize most severe pediatric cases involved unvaccinated children. Hospitals Report Capacity Strain Major Michigan health systems report: Rising emergency visits High inpatient occupancy Increased ICU monitoring While hospitals remain operational, officials caution that continued spread could stress resources. Why This Flu Season Is Especially Concerning Health experts cite multiple factors: Earlier seasonal peak Higher transmission rates Lower childhood vaccination coverage Co-circulation with COVID-19 and RSV Public health officials also warn about rising cases of measles and whooping cough, linked to declining vaccination rates. How to Protect Yourself and Your Family 1. Get Vaccinated Recommended for everyone 6 months and older Still effective against severe illness Not too late to get the flu shot 2. Practice Good Hygiene Wash hands with soap for 20 seconds Avoid touching face Clean high-touch surfaces 3. Stay Home When Sick Do not “push through” illness Keep sick children home from school 4. Use Masks When Necessary Especially when sick or in crowded indoor spaces When to Seek Emergency
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