Fewer people in Colorado are getting their annual flu shots this year, as a new “K” flu variant spreads both in the state and across the United States. According to data from the Colorado Department of Public Health and Environment, about 25% of Coloradans have received their flu shots so far this fall. This is a decrease from 27% at the same time last year and significantly lower than the 32% who were vaccinated during the entire winter respiratory virus season in 2024-2025.
The drop in vaccination rates comes at a time when infectious disease experts are warning about a potentially severe flu season. The Type A H3N2 “subclade K” variant has already caused early outbreaks in countries such as Japan, the United Kingdom, and Canada, and is now spreading in Colorado and other parts of the U.S.
“In the U.S., 20,000 to 30,000 people still die every year from the flu,” said Dr. Michelle Barron, UCHealth’s senior medical director for infection control and prevention. “That’s not insignificant,” added Barron, who is also a professor of medicine and infectious diseases at the University of Colorado School of Medicine on the Anschutz Campus.
The “K” variant may soon become dominant in the U.S. It appears to be more effective at evading vaccines and bypassing immune defenses. Although this year’s flu shot does not perfectly match the “K” variant, Dr. Barron emphasized that vaccination remains important: “It’s never too late. Now that we’re seeing an uptick in flu cases, it’s a great time to go get your vaccine because the numbers will continue to rise,” she said. “You’re going to need that extra level of protection as more people get sick and as more people will be traveling or having visitors.”
Dr. Barron noted that while confusion about vaccines has contributed to declining vaccination rates overall—including for COVID-19—she encourages everyone to talk with their healthcare providers about getting both flu and COVID-19 vaccines.
“Flu is a separate virus (from the one that causes COVID-19),” Barron said. “People are going to get really sick from the flu this year. The very young, the very old and people with underlying medical conditions are at the greatest risk.”
Last year’s flu season was severe nationwide; estimates suggest between 27,000 and 130,000 deaths occurred due to influenza in the U.S., including at least 279 confirmed pediatric deaths according to CDC data.
Regarding how viruses change over time, Dr. Barron explained: “They’re like copying errors… It has a number of mutations. This is common. Flu mutates all the time.” She compared vaccine mismatches to sending mail with an incorrect ZIP code: “You change one number on the ZIP code, and it could send your mail next door, down the street or 50 miles away.”
Despite these challenges, Dr. Barron stressed that current vaccines still provide important protection: “The vaccines still work. Your body will know that the virus is present. But these mutations can evade your immune system… The flu shot still protects you. When it’s a mismatch, you might get sick, but the vaccine decreases the likelihood that you will be hospitalized and decreases the likelihood that you will die from complications of the flu.”
In Colorado, most lab-tested samples currently show infections with subclade “K.” State labs monitor which strains are circulating by analyzing hospital patient samples sent by doctors.
Dr. Barron expressed concern over declining vaccination rates: “We’re seeing a lot less uptake of the flu vaccine than we’ve seen historically, and that’s not a good trend, especially because we know these vaccines (flu and COVID-19) are very good and reduce severity of illness.” She encouraged those with doubts about vaccines to consult their healthcare providers: “The vaccine misinformation is not based on sound science… My hope is that people will still consult with their providers.”
She highlighted particular worry for children: “These were generally healthy kids… Parents may think a flu shot is not a big deal. But even healthy kids have immune systems that are not as mature… It distresses me greatly when parents don’t fully understand risks and don’t get their children vaccinated.”
Her advice remains direct: Go get vaccines for yourself and your children now.
