Timing of Colorado’s COVID peaks is "fascinating and beguiling" – The Colorado Sun

As Colorado slogs through its fourth winter of the COVID-19 pandemic, a curious trend has emerged.

This season at least so far the state reached its peak for hospitalizations of people with COVID in the second-to-last week of November. Thats almost exactly when a peak happened last year. And the year before that. And the year before that.

Four years, four different predominant variants of the virus, four different levels of vaccination and immunity in the population. And four times that COVID hospitalizations began rising in late summer or early fall and, more notably, began to decline in Colorado right around Thanksgiving.

Fascinating and beguiling, is how Elizabeth Carlton, a professor of epidemiology at the Colorado School of Public Health, described the phenomenon.

I think, by now, there probably is something happening driving this pattern, she said instead of the trend being a statistical fluke.

What that something is, though, no one knows.

It is an interesting pattern, said Dr. Rachel Herlihy, the state epidemiologist at the Colorado Department of Public Health and Environment. I dont think we can fully explain it.

As it seems like everyone you know is sniffling or coughing or otherwise testing positive for something, here is what we know about Colorados current COVID trends:

Carlton said its important to remember that even if COVID levels are falling or arent as severe as in prior years, we are still in the middle of the high season for all kinds of respiratory illnesses such as flu, RSV and that weird hacky-cough virus going around this year that no one can quite seem to identify.

That means people should continue to take precautions, such as staying home if theyre not feeling well, seeking treatment when sick and considering wearing a mask in crowded places. Its also not too late to get vaccinated with an annual flu shot, an updated COVID booster or, if eligible, an RSV vaccine.

Colorados late-November COVID peaks are unusual because they tend to happen earlier than peaks across the rest of the country. Last year, hospitalizations peaked nationally in January, same as the year before.

They have also sometimes had the effect of blunting the arrival of a new variant. When a new variant called XBB.1.5 swept across the country last year, it had little impact in Colorado, perhaps because our earlier-breaking wave had built up a layer of fresh immunity in the state.

This is not always the case. In early 2022, Colorado saw a significant rebound in infections and hospitalizations in January, driven by the arrival of the original omicron variant. This years trends may prove to be a smaller-scale version of that.

But the November peak has remained a COVID constant in Colorado, sticking to a much tighter turnaround schedule than other respiratory viruses like the flu, which sometimes hits early and sometimes later in winter. It is also intriguing because, with holiday travel in late November and December, one would normally expect to see cases increasing as a result.

Carlton said shes thought of a few theories that might help explain the peaks. One possibility is weather patterns viral transmission changes as temperature and especially humidity levels do, with drier air more favorable to infection.

Were just a drier state and we know this virus seems to spread under dry conditions, she said.

The school calendar may have an impact. Colorados school year tends to start earlier than in some other states. Mobility and travel habits may also play a role say, more people heading to the mountains to go skiing or spending more time indoors.

But none of these quite fits either, she said. Some falls have been wetter than others over the past four years. And, in order for hospitalizations from COVID to start falling in late November, infections would need to begin slowing at least a couple weeks prior, before ski season and school breaks really start.

Four winters in and there is still so much left to learn about this virus.

I think what COVID has taught us is that it evolves incredibly rapidly, Carlton said. So what we think we know today may change by tomorrow.

Based on facts, either observed and verified directly by the reporter, or reported and verified from knowledgeable sources.

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Timing of Colorado's COVID peaks is "fascinating and beguiling" - The Colorado Sun