The 2025–2026 flu season has been one of the worst in over a decade. The CDC classified the season as moderate overall, but that label masks what’s happening to children: pediatric severity is rated high, with hospitalization rates for kids not seen since tracking began in 2010. By mid-March, the cumulative hospitalization rate across all ages hit 81.6 per 100,000, the third highest in 15 years of surveillance.
This Season by the Numbers
Influenza A(H3N2) has dominated this season, which matters because H3N2 years tend to hit harder than H1N1 years. A new subclade of H3N2, informally called “subclade K,” was first identified in August 2025 and has been growing as a proportion of circulating viruses. H3N2 strains are historically associated with more severe illness in older adults and young children, and this season is following that pattern.
By late January 2026, 27 U.S. states and jurisdictions were reporting high or very high flu activity, with 7 at the “very high” level. Hospitalizations climbed steeply through the winter, peaking in late December when the weekly pediatric hospitalization rate reached 7.0 per 100,000, the highest single-week rate for children recorded since the 2010–2011 season.
Through mid-March, 115 children had died from flu-related illness this season. For comparison, the entire 2024–2025 season saw 293 pediatric deaths, meaning this season’s toll was already substantial with months of data still being collected.
Children Are Hit Especially Hard
While the CDC rates both adults and older adults at moderate severity, the pediatric age group stands apart. Children under 18 have the second-highest cumulative hospitalization rate (41.0 per 100,000) since 2010, and their peak weekly rate was the single highest on record for the surveillance period. This isn’t a small statistical difference. It reflects a season where emergency departments and pediatric wards saw an unusual surge of seriously ill kids.
H3N2 seasons often produce higher hospitalization rates in both the very young and adults over 65. This year, children bore a disproportionate burden compared to other age groups. If your child develops a high fever, difficulty breathing, or symptoms that improve and then return with fever and worsening cough, those are signs the illness may need medical attention.
How Well the Vaccine Worked
Interim data from California found the flu vaccine reduced the chance of testing positive for flu by about 33% across all ages. That’s a modest number, though not unusual for an H3N2-dominant season, since H3N2 viruses are notoriously harder to match with vaccines.
Protection varied by age. Children and teens got the most benefit at 39% effectiveness. Adults 18 to 49 saw 34%, adults 50 to 64 saw 31%, and adults 65 and older got the least protection at just 22%. For older adults, the type of vaccine mattered: recombinant vaccines provided 39% effectiveness, roughly double the 16% seen with standard-dose shots. Adjuvanted and high-dose vaccines, often recommended for seniors, landed at 22%.
For children ages 2 to 17, the nasal spray vaccine outperformed the standard shot, with 55% effectiveness compared to 39%. Even at 33% overall, vaccination still reduces the risk of severe illness, hospitalization, and death beyond what these headline numbers suggest, since effectiveness against the worst outcomes is typically higher than effectiveness against any infection.
Antivirals Still Work
One piece of good news: the viruses circulating this season remain overwhelmingly responsive to antiviral medications. Out of more than 3,500 viruses tested, none showed resistance to baloxavir (sold as Xofluza) or zanamivir (Relenza). Only 0.6% of tested viruses showed any reduced response to oseltamivir (Tamiflu), and those were limited to a specific subset of H1N1 viruses, not the dominant H3N2 strain.
Antivirals work best when started within 48 hours of symptom onset. They can shorten illness by about a day and, more importantly, reduce the risk of complications like pneumonia. For people at high risk, including young children, adults over 65, pregnant women, and those with chronic conditions, early antiviral treatment can make a meaningful difference in outcomes.
Bird Flu Remains a Separate Concern
If you’ve seen headlines about H5N1 bird flu, that’s a different situation from the seasonal flu. No confirmed human H5N1 cases have been reported globally in 2026 so far. The U.S. has investigated several possible H5 cases, but the CDC has been unable to isolate the virus from recent suspected cases or confirm the subtype. H5N1 is not spreading between people, and it is not contributing to the seasonal flu burden you’re experiencing or hearing about in your community.
What This Means Practically
This has been a notably bad season, particularly for families with young children. The combination of a dominant H3N2 strain, a new and spreading subclade, and lower-than-ideal vaccine effectiveness created conditions for high hospitalization rates. If you or your child develop flu symptoms, antiviral treatment is available and effective for this season’s viruses, but the window to start it is narrow. Getting tested early matters, especially for anyone in a higher-risk group.
Flu seasons vary widely from year to year, and the severity of this one doesn’t predict what next year will look like. But it does underscore why this season felt worse than recent ones: for many age groups, and especially for children, it genuinely was.