With almost 800 hospitalizations statewide last week, Colorado is in the throes of its worst flu surge in almost a generation, less than midway through a season of sickness doctors say they worry hasn’t yet bared its full fangs.

“We’ve definitely seen an increase in the flu, and I think over the last two to three weeks we’ve seen an increasing number of patients showing up who are sicker with the flu,” said Dr. David Steinbruner, chief medical officer and an emergency medicine physician at UCHealth Memorial Hospital in Colorado Springs.

As of Tuesday, UCHealth reported having 152 influenza patients across its Colorado network, compared to 114 during the worst week of last year’s respiratory virus season, in February.

“We’ve already surpassed that, and we’re not sure that we peaked yet,” Steinbruner said. “And I think we’re not expecting to see it (peak) for some time, which means we could be in for a really bad flu season … if we’re already at those numbers across the system.”

According to the Colorado Department of Public Health and Environment (CDPHE), which tracks and reports hospital admissions for influenza, respiratory syncytial virus (RSV) and COVID-19, the last week of 2025 set a grim bar.

“Although the cumulative hospitalization rate to date is slightly lower than what was seen at this same time in the 2022-2023 season, the 782 new flu-related hospitalizations reported for the week ending Dec. 27 is a record for raw numbers of influenza hospitalizations reported in one week since we started tracking influenza hospitalizations in 2004,” said Hope Shuler, a spokesperson for CDPHE’s Division of Disease Control and Public Health Response.

Flu hospitalizations in El Paso County for that same week were more than double last year at this time, 88 compared to 36, according to the most recent data from El Paso County Public Health.

Yes, it is that bad, officials said.

Flu hospitalizations rose dramatically in many places around the nation over the closing weeks of 2025, but, as of Dec. 27, Colorado was among five states – with New York, New Jersey, South Carolina and Louisiana – where the spike in viral activity led the Centers for Disease Control and Prevention (CDC) to set flu DEFCON to the highest echelon of “high risk.” 

“Flu season doesn’t hit every state at the same time or with the same intensity,” Shuler said. “Typically, we see cases rise first in the Southeast — as we did this year in Louisiana — but the flu is unpredictable and can start anywhere.”

Phoebe Lostroh, an associate professor in the Department of Molecular Biology at Colorado College – and the author of a textbook on viruses and virology – said there are no clear indicators as to why Colorado is at the tip of this season’s especially virulent and destructive strain of influenza.

The holidays and cold weather traditionally draw large groups together in confined spaces, which is why flu numbers always tend to rise around this time of year. But such seasonal situations aren’t unique to Colorado, which, incidentally, is experiencing one of its warmest holidays on record.

And while flu immunization rates in the state are down slightly from last year – 27.5% of Colorado residents had received a flu vaccine as of Dec. 27, compared to 28.8% this time last year, according to CDPHE – fractional downshifts don’t equal the tsunami of illness sweeping across the Centennial State.

“No one has been floating any theories as to why certain states are worse than any others at this particular time,” said Lostroh. “But I think everyone is concerned that it’s going to get bad everywhere and we’re just bellwethers. 

“Other states should not be feeling confident, like they escaped. It just hasn’t gotten to them yet.”

Young children and older adults – especially those who are unvaccinated and who have other health conditions that weaken their immune systems or resiliency – traditionally represent the majority of flu cases requiring hospitalization, and which, unfortunately, turn fatal.

“What’s really been bothering me is the pediatric deaths,” Lostroh said. “That’s terrible to have pediatric deaths from the flu outside of a pandemic year.”

The first pediatric death from influenza in Colorado, and among the first in the nation, was a Denver-area elementary school child, who died in mid-December, according to CDPHE. Almost 300 pediatric patients succumbed to the flu nationwide during the 2024/25 flu season, according to the CDC, which, as of late December, reported eight influenza-related deaths among children and estimated more than 3,000 people of all ages had died from the flu so far this viral season.

Vaccinations remain the best way to defend bodies of every age against the worst effects of seasonal viruses, said Steinbruner.

“People have hesitancy in taking vaccines, and I think sometimes they don’t quite understand the purpose of the vaccine for the health of the whole population,” he said.

A flu vaccine doesn’t make a person immune from illness, but the shots have been proven to stave off the worst symptoms, which lead to the worst outcomes, Steinbruner said.

“It’s really important for people to understand that every little bit helps and that the vaccines are very safe and oftentimes very effective,” he said.

Steinbruner recalled an ER encounter he’d had a few weeks prior with an unvaccinated flu patient who became very sick and required hospitalization, and the teachable moment, he said, that the visit also provided.

“That person’s family member had been vaccinated and they were not sick at all,” Steinbruner said. “I think it really speaks to the fact that, you know, prevention is the key.”

Wash your hands. Stay home when you’re sick, and wear a mask if you absolutely must go out, experts said.

And, oh, yeah — get vaccinated, they emphasized.

“Anything that can help prevent the spread of this is going to help all of us to get through this better,” Steinbruner said.