Pediatricians are asking parents to prioritize getting their families vaccinated after Colorado set back-to-back records for children’s flu hospitalizations in the two most recent seasons.
So far in the 2025-26 season, which officially wraps up Saturday, Colorado reported 1,169 hospitalizations of people under 18 for the flu — the highest toll since the state started tracking those numbers. That number still could grow slightly in the week before the 2026-27 season starts.
The previous season, which started in October 2024, also set a record at the time, with 856 pediatric flu hospitalizations.
died of flu complications this season, which was the highest toll since 2009-10, when a new variant of swine flu swept the world. That year, 12 children died, tying it with 2003-04 for the deadliest season for children in the state since reporting started.
Last year, the H3N2 strain of influenza A, which tends to be more severe, was the most common version of the virus, said Dr. Suchitra Rao, an infectious-disease specialist at Children’s Hospital Colorado. In addition, the strain picked up a few mutations that made the vaccine less effective, and the vaccination rate dropped, meaning fewer kids had even partial protection, she said.
About 37% of Colorado children from 6 months to 9 years old , as did about 25% of older children and teens. The Centers for Disease Control and Prevention reported about between 6 months and 17 got the shot.
Children’s alone had more than 900 kids hospitalized with flu in the most recent season, and about 800 during the one before, Rao said. They were able to staff up and care for every child who needed a hospital bed, she said.
Although the exact percentage varies from year to year, don’t have a known medical condition that puts them at high risk.
“Flu can kill. It’s not just something that gives you a mild runny nose and is inconvenient for a few days,” Rao said.
Outpatient providers also had an unusually busy respiratory season.
Dr. Deniz Kolozs, associate medical director of pediatrics at Kaiser Permanente’s Aurora Centrepoint location, said the system’s Colorado clinics had to increase staffing and spend more time coordinating with hospitals during the peak of flu season last December.
She attributed much of the increase in illnesses to low vaccination rates.
“We had doctors working overtime,” she said.
Children under 5 are at increased risk from flu, with the greatest danger for babies under 6 months, who can’t get vaccinated, Kolozs said. Young children have smaller airways and are at a higher risk of dehydration, and parents may not always recognize how sick they are if they don’t have enough language to describe their symptoms, she said.
Obstetricians recommend that pregnant women get the flu shot to pass partial immunity to their babies and that people who spend time with infants also get vaccinated, to reduce the odds they’ll pass the virus along.
The country as a whole had higher-than-expected hospitalizations and deaths from flu the past two years. In both seasons, the was about 23% higher than in the next-most-severe year, and roughly twice the median rate for the last 16 years — the point where half of years were worse and half were better.
In the most recent flu season, 193 children died of flu complications nationwide, . The previous year, 2024-25, had the highest flu death toll for children since at least 2004, with 297.
The most common reason that children end up hospitalized from the flu is pneumonia and other respiratory problems, whether from the virus itself or from opportunistic bacteria, Rao said. Young children are also vulnerable to dehydration, and a small share of kids develop organ inflammation while they’re fighting the flu, she said.
The flu season is always unpredictable, but the United States can get a few clues from the Southern Hemisphere, which has its flu season during our summer. The season appeared mild at first, but Australia is having a late surge in severe illnesses, Rao said.
One positive sign, however, is that the flu vaccine seems well-matched to the circulating strains this year, she said.
The flu shot is the most important defense against severe illness and is partially effective in preventing milder cases, Rao said. Antiviral medication can also help prevent complications, particularly if people take it in the first few days of illness, she said.
Kolozs urged people to get vaccinated soon, rather than trying to time their shot for maximum immunity around the holidays. It takes roughly two weeks for the immune system to respond, and no one can be sure when the virus will start circulating widely, she said.
“Influenza makes people very, very sick,” she said. “The good news is, we have a safe and effective tool to protect everyone.”
