Fewer people in Colorado are getting their annual flu shots this year, even as a new and concerning “K” flu variant spreads across the state and the U.S. According to the Colorado Department of Public Health and Environment, only about 25% of Coloradans have received their flu shots so far this fall. This marks a decrease from 27% at this time last year and is notably lower than the 32% who were vaccinated during the entire winter respiratory virus season in 2024-2025.
The decline in vaccination rates comes as public health officials warn that the Type A H3N2 “subclade K” variant is now circulating widely. This strain has already led to significant outbreaks in countries such as Japan, the United Kingdom, and Canada. Infectious disease experts caution that these developments could result in a difficult flu season.
“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,” said Barron, who is also a professor of medicine and infectious diseases at the University of Colorado School of Medicine on the Anschutz Campus.
Dr. Barron noted that while this year’s flu shot does not perfectly match the new “K” variant, it still offers important protection against severe illness or death from influenza. She advised: “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. 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.”
She added: “The worst part of the holiday season is if you’re sick and stuck in bed. You want to be able to go out and enjoy the holidays.”
Dr. Barron attributed falling vaccination rates partly to confusion about vaccines overall—a trend she says makes it easier for viruses like influenza to spread within communities. She emphasized that both COVID-19 and influenza are separate viruses requiring different vaccines: “Flu is a separate virus (from the one that causes COVID-19). 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 saw high levels of severity during flu season nationwide; estimates indicate between 27,000 and 130,000 deaths due to influenza in the U.S., with at least 279 confirmed pediatric deaths according to CDC data—most among previously healthy children.
The H3N2 strain responsible for most current cases has mutated more than usual this year, giving rise to what experts call copying errors or mutations—specifically resulting in subclade K. Vaccine manufacturers had already produced this season’s shots before these changes became apparent; thus, while there is some coverage against H3N2 strains generally, there may be reduced effectiveness against subclade K.
“The vaccines still work. Your body will know that the virus is present. But these mutations can evade your immune system,” Barron explained. “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.”
State laboratory testing confirms most recent samples are indeed subclade K strains.
Barron expressed concern over declining uptake not just for influenza but other vaccines as well: “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 urged those with doubts about vaccination safety or efficacy to consult directly with healthcare providers: “The vaccine misinformation is not based on sound science, and it’s causing a lot of distrust,” she said.
Reflecting on what worries her most heading into peak respiratory virus season—and referencing last year’s pediatric fatalities—Barron said: “These were generally healthy kids… 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 kids now.
