Colorado’s respiratory virus season is most normal since pandemic

Colorado is so far experiencing its most typical respiratory virus season since the start of the pandemic, but no one knows whether the bugs have any tricks to pull over the winter months.

In the winters of 2020 and 2021, COVID-19 raged while influenza and respiratory syncytial virus — or RSV — essentially took some time off.

Last year, with most precautions gone, the other viruses made their seasonal appearance earlier than they usually do, and RSV overflowed pediatric hospital beds as young children went through their first bout with it. While most people only develop a cold when they get RSV, it can be severe for babies, toddlers and older adults.

As of mid-December, flu and RSV are causing relatively normal levels of illnesses and hospitalizations, though both virus’ spread is still increasing, state epidemiologist Dr. Rachel Herlihy said.

COVID-19 hospitalizations have plateaued for the moment, but since the virus hasn’t settled into a typical seasonal pattern, no one can predict what it will do next, she said.

“I think it’s still difficult to say how the season will play out,” she said. “It’s difficult to know when flu and RSV are going to peak, and how high the peak will be.”

The most recent state data on the prevalence of respiratory diseases is from Dec. 3. At that point, emergency room visits for flu were still rising. Two major flu strains, known as influenza A and B, are circulating now, though A is dominant, Herlihy said. Sometimes influenza B causes a second wave of illness after the influenza A wave has petered out, but other times it doesn’t, she said.

RSV hasn’t caused the same wave of illness that strained hospital capacity for children that it did in 2022. So far, the level of hospitalizations at certain hospitals in the Denver area is comparable to the peak in the 2019-2020 season. (The Colorado Department of Public Health and Environment didn’t collect statewide data until this year, which limits comparisons over time.)

Though it doesn’t get the attention it once did, COVID-19 still puts more people in the hospital than either flu or RSV. Since Oct. 1, COVID-19 has hospitalized 2,938 people in Colorado, which is more than twice as many as flu and RSV put together. It has improved over time, though: The state health department showed 260 people were receiving hospital care for COVID-19 as of Tuesday, compared to 395 at the same time last year.

While COVID-19 hospitalizations in Colorado have tended to peak in late November or early December, the virus hasn’t firmly settled into a pattern, Herlihy said. It continues to evolve new variants that are better at avoiding the immune system and have the potential to increase cases again, she said.