Flu hospitalizations have spiked to record levels this winter in Colorado.

And while it’s early in the 2025–26 flu season, flu outbreaks have been rough both globally and in the United States. So far, according to officials with the U.S. Centers of Disease Control and Prevention (CDC), the flu this season has caused at least:

• 11 million illnesses
• 120,000 hospitalizations
• 5,000 deaths, including at least nine among children

And in Colorado, the flu has sent thousands of people — both adults and children — to clinics and hospital ERs.

So far, according to experts at the Colorado Department of Public Health and Environment, the 2025–26 flu season in Colorado has caused:

• More than 3,227 hospital admissions in Colorado since Oct. 1, 2025
• Positivity rates as high as 33% for flu
• And one pediatric death in Colorado this winter

In Colorado, fewer people are getting their flu vaccines. As of early January 2026:

• About 28% of Coloradans have gotten a flu vaccine, down from about 29% at the same time last year and significantly lower than the total number of Coloradans who were vaccinated last year.
• Among Coloradans who have gotten a flu shot so far this year, older adults are most likely to have received one, but the rates remain low.
• About 50% of Coloradans ages 65 and older have gotten a flu shot during the 2025 and 2026 season.
• About 31% of babies and children under age 10 have gotten their flu vaccines in Colorado.
• And fewer than 15% of Coloradans in their 20s have gotten a flu shot.

What’s happening with the flu at UCHealth hospitals now?

Why has this winter’s flu season been so severe?

What is the cause of this record-setting surge in flu hospitalizations, and why has this year’s flu season been so bad?

“It’s a perfect storm,” said Dr. Michelle Barron, senior medical director of infection prevention and control for UCHealth.

“We have low vaccination rates, and we have a more virulent, more transmissible strain, said Barron, who is also a professor of medicine and infectious diseases at the University of Colorado School of Medicine on the Anschutz Campus.

The flu strain that has hit hard this year is the subclade “K.” (Read more about the “K” flu strain.)

The timing for the “K” strain’s surge in Colorado was especially bad.

“Fewer people were vaccinated, and people were gathering over the holidays. Then, kaboom, it hit,” Barron said.

To learn more about this year’s flu spikes, we asked Barron some of your top questions about this year’s flu strains, how you can protect yourself and your family and what to do if you’re feeling sick.

Why did flu cases surge so quickly in December 2025?

Flu is predictable. It arrives at the same time every year during what we now call the winter respiratory virus season. Infectious disease experts, like Barron, know to expect surges as we head into the fall and winter. But Barron and other medical professionals never like seeing a dramatic increase in cases like the one that showed up in late November and December 2025 in Colorado as a nearly vertical line, meaning flu infections and hospitalizations shot up suddenly.

“There was no subtlety this year,” Barron said. “When numbers started going up, I thought, ‘OK, flu is circulating.’ But then the slope rose steeply. You don’t ever want a steep line like that.”

Barron said medical providers and hospital pros are keeping up with waves of sick people who are flooding into primary care clinics and hospital ERs. So, if you’re feeling lousy, you should definitely seek help from your medical provider as soon as possible.

What can you do if you’re feeling sick and you think you have the flu?

If you are experiencing flu symptoms, there are multiple steps you can take:

• Call your medical provider right away to get help.
• You can get tested to learn exactly what you have, whether it’s flu, COVID-19 or RSV.
• If you test positive for the flu, there’s a treatment called Tamiflu that can shorten the duration of your illness. But you need to start taking Tamiflu early in the course of the illness.

Can I still get a flu shot?

Yes. Barron said it’s not too late to get your flu shot. Adults should protect themselves, and parents should be sure to get their children vaccinated. Here’s key information from Barron and others about flu shots:

• Everyone 6 months of age or older should get a flu shot.
• There are special, stronger versions of flu vaccines for older people and those who are immunocompromised.
• Call your doctor’s office or head to a nearby pharmacy and get your flu shot now.
• In recent years, the U.S. has experienced strange spikes in flu cases in the spring. If you get a flu shot soon, you can protect yourself during the remainder of the winter respiratory virus season and throughout the spring.

During flu season, if you haven’t gotten sick yet, you can also do everything you can to stay healthy and avoid getting the flu or other illnesses and spreading them to other people.

“What can you do? Get your shot. Wash your hands. Clean surfaces. Stay home if you’re sick. Wear a mask. Masks are protective, especially if you’re in a household where flu is running rampant,” Barron said. (Learn why soap and water work better than hand sanitizer when it comes to staying healthy.)

What should I do if someone in my house has the flu? Should I wear a mask? And should I take Tamiflu to prevent a flu infection?

Yes, you can take Tamiflu if you’ve been directly exposed to the flu.

Barron has a friend who called her for advice. His young child got sick with the flu at day care. The parents had been too busy to get flu vaccines for their child or themselves. The parents are immunocompromised and wondered how they should protect themselves. Should they consider taking Tamiflu — the medication that people can take early in the course of a flu infection to reduce the severity of the flu or to shorten the course of the illness?

Barron’s advice to her friend was simple and clear.

“Yes. You have diabetes. So, you’re at higher risk if you get the flu. You can take Tamiflu.”

She said people who have the flu in their home or who were otherwise exposed and are at high risk for severe illness if they get the flu can take Tamiflu prophylactically to prevent flu cases.

If you’re feeling sick, or a member of your household is sick, it’s wise to get tested for flu, COVID-19 or RSV and check with your medical provider about medications you can take.

“Tamiflu can help. You still want to do everything to try and avoid contact with the person who is sick while they’re infectious, like wearing a mask in your home,” Barron said.

She also advised her friend to have the whole family get flu shots once their child recovered.

If I didn’t get a flu shot and either a family member or I already got the flu, should I still get a flu shot?

 Yes. Barron said that if you didn’t get a flu shot this winter — for whatever reason — it’s still wise to go get the vaccine.

Like many people, Barron’s friends were confused about whether they should get flu shots for themselves or their child after going through one bout of the flu. They assumed that their child had immunities to the flu since she had already gotten a confirmed case of it.  And presumably, they had been exposed as well. Should they still get a flu shot?

“Yes. All of you need the flu shot,” Barron told her friend. “Your daughter had Type A flu (presumably the “K” subclade), but she hasn’t had Flu B yet, and she’s in daycare, so she’s exposed to a lot of viruses.”

Since the parents had been on Tamiflu, Barron advised them to wait at least 48 hours after finishing the medication, then they should get their flu shots. Since their child had the flu, Barron recommended waiting about two weeks after the child recovered, then taking the daughter to get her flu shot.

“Don’t forget to get the shot. You don’t want to miss the opportunity (to get the protection). She has immunity to Flu A. But she doesn’t have immunity to Flu B. And we don’t know exactly when it’s going to start circulating. What are the chances that she’ll get flu again? We don’t know exactly. But it’s a risk, and getting the flu is no fun at all.”

So, is it possible to get the flu twice in the same flu season?

Yes. Barron said it is possible to get two different strains of flu during the same season. The best way to avoid getting the flu — or to avoid getting severely ill and needing to be hospitalized with the flu — is to get your vaccine.

We’ve experienced a big spike already with the subclade K version of Type A flu. When do Type B flu infections typically start spreading?

Type B flu strains typically start spreading in the late winter or in the spring and sometimes even in the summer, Barron said.

“We’re still very much in flu season here. We’re not done yet. And Flu B will pop up soon or in the spring,” Barron said.

“Typically, we start seeing Flu B in March, which is why I’ll say it a thousand times: ‘If you have not gotten your flu shot, you need to go get it.’ We’re in the thick of flu season. And everyone will benefit from getting that protection.

“Even if this year’s shot is not a perfect match for the strains that are circulating this year, getting a flu shot still decreases the severity of illness. You don’t want to be off from work or have kids out of school for a long period of time. You don’t want to be hospitalized.

“And flu is hitting kids hard this year. There have been quite a few pediatric flu deaths. Even healthy kids can get complications from the flu,” Barron said.

Who is most at risk if they get severely ill from the flu?

“We talk a lot about the very old and the very young and people who have underlying health conditions,” Barron said. “But young, healthy children die from the flu. And for some reason, this year’s strains seem to be very hard on kids.”

Are flu cases starting to go down in Colorado now?

Data from the Colorado Department of Public Health and Environment show that there has been a slight dip in flu hospitalizations early in 2026 since December 2025 peaks. But Barron and fellow infectious disease experts know from experience that flu cases often come in waves. She and other medical pros are bracing to continue caring for people with the flu for several more weeks.

“Flu is still circulating. It hit early in Colorado and places like Louisiana and New York. Now, everyone else is getting hit, and people are traveling. We have visitors from all over the world, so new potential exposures are happening all the time.”

Are this year’s flu strains causing different symptoms this year?

No. The symptoms are typical. People feel lousy. They often have a fever and a cough. Flu hits suddenly, and people can have body aches.

“It’s typical for the flu. The ‘K’ strain seems to spread faster, and you may feel sicker, but the symptoms are the same,” Barron said.

What happens when people need to be hospitalized with the flu?

Some children and adults need to be hospitalized with the flu when they have trouble breathing or get severely dehydrated.

If you or your child is ill, do not delay. Call for help right away.

Barron said some people can develop bacterial pneumonia on top of a flu infection.

“And what gets people in trouble (and can be deadly) is breathing issues,” Barron said.

Are there other typical symptoms of the flu?

Yes. Along with chills, fevers and a cough, people can have a runny nose, a sore throat and a headache, Barron said.

What should you do if you’re feeling sick and you think you might have the flu?

If you are experiencing flu symptoms, check with your medical provider right away. You can get tested to learn exactly what you have, whether it’s flu, COVID-19 or RSV.

If you test positive for flu, you can take Tamiflu. But you need to act quickly. You need to start taking Tamiflu early in the course of the illness.

Be sure to stay hydrated. You can use home remedies to feel better. Be sure to keep essential medications on hand at home so you don’t have to venture out when you feel lousy.

And you can comfort yourself or others who are feeling sick by making soothing soups. Check out some soup ideas to make during flu season.

Remind me of the basics. What exactly is the flu?

The flu is a respiratory illness caused by the influenza virus. There are three types of the virus, but only two (influenza A and influenza B) are responsible for the annual flu season, which can stretch from September through April.

The disease is highly contagious and spreads primarily through respiratory droplets from person to person when people sneeze or cough. The virus changes from year to year. That’s why we need a new flu shot every year.

What about pregnant women? Are they also at risk if they get the flu?

“Yes. If you’re older or very young, or you have underlying medical conditions that impact your immune system, you’re at higher risk,” Barron said.

Yes. Pregnant women, like the very young, the very old and people with underlying health conditions, are at high risk of getting the flu and getting severely ill.

“We’ve been seeing higher rates of pregnant women becoming infected and hospitalized with influenza and other illnesses,” Barron said.

Misinformation has reduced vaccination rates during pregnancy.

“Some people think, ‘I’m young. I’m healthy. Why would I need a vaccine?’ But they’re not thinking about the fact that when you’re pregnant, your immune system is not as strong,” Barron said.

She strongly advises pregnant women to get all of the recommended vaccines.

What should people do to protect themselves from the flu and other winter respiratory viruses?

The answer is very simple: get vaccinated.

“We have many very good, very safe, very effective vaccines,” Barron said.

Each year, the effectiveness varies because vaccine makers have to guess in advance exactly which variants of each virus will be spreading much later. But even if the flu vaccine is not a perfect match, it will help protect people from hospitalization and death.

“The vaccines do not necessarily keep you from getting sick, but they decrease severity. So, if you get a flu vaccine, you are much less likely to end up in the hospital,” Barron said.

“The other reason it’s important to get your shots is that you will be in contact with other people: from family members to co-workers and friends. If you don’t get a vaccine, and you get sick, you’re much more likely to give an infection to someone else,” Barron said.

“You may be young and healthy, but that doesn’t mean that everybody around you is also healthy, and you want to protect them,” she said.

What else can people do to stay healthy and avoid getting the flu?

The basic rules for staying well apply. Whether you’re trying to avoid getting sick from the flu, COVID-19, RSV or the common cold, Barron advises people to take the following precautions:

• Wash your hands frequently with soap and water.
• Cover your cough.
• Stay home if you’re sick. Don’t spread illnesses to other people.
• If you can’t wash your hands with soap and water, use hand sanitizer. But remember that sanitizer doesn’t kill viruses that cause stomach bugs, like norovirus. To kill these bugs, you must use soap and water or bleach.
• Clean surfaces frequently. (Barron keeps bleach wipes handy.)
• Clean your devices. If you have washed your hands, but not your phone, and you touch your phone, then eat, you can get sick.
• If your hands aren’t clean, avoid touching your face, eyes or nose, as you can spread viruses.

I skipped getting a flu vaccine. If I get one now, how long will it take for the vaccine to fully take effect?

“It’s not too late to get your flu shot,” Barron said. “Flu season typically runs through March, sometimes as late as April or May. So even though we’re seeing a spike now, we haven’t yet seen influenza B.

“We typically start to see influenza B right around spring break,” Barron said.

If you feel lousy, you’re not alone.

Influenza cases are spiking now in Colorado and across the U.S.

Many people are suffering with chills, fevers, a cough, runny nose, sore throat, headache and body aches. While those symptoms can also be consistent with COVID-19, experts say influenza A cases are dominating the winter respiratory virus season right now. (Don’t confuse influenza with extremely contagious stomach bugs, like norovirus, which some people also call the stomach flu.)