Colorado has wrapped up its first relatively ordinary respiratory disease season since the pandemic began, with no unusually large or strangely timed spikes in illness.
But with COVID-19 still in the mix, this new normal still means a higher level of severe illness and death than the state experienced before 2020.
In the fall of 2020 and 2021, Colorado and the country as a whole saw large waves of COVID-19, but almost none of the usual illnesses from flu and respiratory syncytial virus. RSV causes colds for most people, but can be severe for babies and older people, particularly those with other health conditions.
In the fall of 2022, COVID-19 didn’t cause as much destruction, but a spike in RSV sent an unusual number of Colorado kids to hospitals, possibly because a large cohort of younger children hadn’t gotten infected while people around them were taking respiratory precautions. That year’s flu season also started unusually early.
This year, flu and RSV hospitalizations started to take off in Colorado in October and peaked in late December, which is roughly when hospitals expect increased virus activity, said Dr. Michelle Barron, senior medical director of infection prevention and control at UCHealth.
The state’s COVID-19 hospitalizations followed a similar trajectory, though they started rising in the summer and peaked a few weeks before the other viruses.
“I would never say ‘normal,’ because every time I say normal there’s a new normal… but it was more typical” compared to recent respiratory virus seasons, Barron said.
Yet even in a relatively average season, significant numbers of people get sick.
Between October and early May, the Colorado Department of Public Health and Environment reported:
6,333 COVID-19 hospitalizations
3,939 flu hospitalizations
3,828 RSV hospitalizations
This winter wasn’t a particularly severe flu season in terms of the number of people hospitalized or how ill they became, Barron said. The number of people hospitalized could have been lower, though, if more people had gotten vaccinated against respiratory illnesses, but fatigue with talking about viruses seems to have depressed uptake, she said.
COVID-19 had its mildest season yet, with 280 people hospitalized statewide at the peak in late November, compared to 1,847 at the worst point in December 2020.
Flu, in contrast, set its second-highest peak since the 2018-2019 season — though that period includes two years with minimal flu activity.
RSV is more difficult to compare over time, because Colorado’s health department only started tracking statewide data this year. It has looked at RSV in a selection of Denver-area hospitals since at least 2018, though. This year’s peak was the second-highest in that time, though the hospitalization rate was one-third lower than in the unusually severe 2022-2023 season.
COVID-19 killed far fewer people than in previous seasons, but still claimed 647 lives in Colorado between the start of October and the end of April. Three children died of flu this season, and none died of RSV. The state doesn’t track flu and RSV deaths among adults.
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Of the three major respiratory viruses, COVID-19 still has the highest death rate, though the gap has narrowed now that almost everyone has been vaccinated, survived it or both.
A study by the U.S. Department of Veterans Affairs earlier this year found that veterans hospitalized with COVID-19 were about 35% more likely to die than those hospitalized with flu. The group studied was older and almost entirely male, however, so it may not reflect comparative risks for the general population.
During the early years of the pandemic, COVID-19 would surge multiple times throughout the year, but it seems less likely to do that now, Barron said. That could change if a significantly different variant evolved, but all of the current types circulating are descended from omicron, she said.
“I think we’re inching closer” to a more predictable virus, she said.
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