It's the season for colds and flu, but this year is shaping up to be one of the worst flu seasons many doctors have seen in more than a decade.

"We're having a lot of kids coming in very sick," said Dr. Olukemi Akinrinola, a pediatrician at AdventHealth in Parker. "This year we're noticing a big spike and influenza A and we're not really sure why."

Akinrinola believes vaccine hesitancy may be partially to blame. Some of her sickest patients, she said, are those who are not vaccinated for influenza.

"When they get into the room, they are lying down, they're so sick, lethargic, high fever," she said. "And almost always they are the kids that haven't gotten the vaccine."

And it's not just the flu that is spiking in Colorado.

"We also have other viruses that are spiking like RSV, COVID-19, norovirus," explained Akinrinola. "And there's been a strain of strep that's also come up."

The latest data from the Colorado Department of Public Health and Environment shows there are at least 150 pediatric patients hospitalized with either COVID-19, flu or RSV. Akinrinola said there days when her clinic is overwhelmed.

"There was a day I saw about 20 (patients) in my clinic, in a day, so it was a bit alarming," she said. "It's like, is everyone seeing what we're seeing?"

Colorado is not alone in this high rate of respiratory illness as many states are also seeing big spikes in cases, according to the Centers for Disease Control and Prevention. In some states, flu is overwhelming their hospitals and forcing schools to close. It's Akinrinola's suspicion that people are likely going to work or school when they're not healthy, and it's spreading the viruses like wildfire.

"So, parents feel like their kids are never well because it's like back-to-back illnesses, but that's because they're not having a break to get their immunity back," she said.

Doctors say people should be getting the flu shot every year, especially high-risk groups. While flu season typically peaks in February, Akinrinola said it's really becoming a year-round virus, and it's not too late to get the vaccine.