Colorado’s COVID trends just broke a pattern that had occurred every fall since 2020

‘Tis the season in Colorado to be hip-deep in people in the hospital with COVID-19 — except not this year.

In each of Colorado’s previous four years living with the virus, the state has seen COVID hospitalizations surge in the late summer and through the fall, with a peak just before Thanksgiving that gradually recedes.

It may not have been the peak for the entire year, but it was a clear spike that ebbed when, during a season of holiday travel and gatherings, you might think it would continue climbing. (And there’s only been one year — the year that the original omicron variant emerged — where it wasn’t the peak.)

The pattern is clear in this chart, versions of which The Sun has run before when writing (and writing) about a phenomenon one epidemiologist has called “fascinating and beguiling.”

But 2024 seems to have broken the trend — COVID hospitalizations are relatively low right now and there was at best only a teensy weensy peaklet just before Thanksgiving. And that may point to ways the virus’s place in our lives is changing and how the ways we track it must also change.

A summer fling with the FLiRTs

The most obvious reason for this deflated COVID season is that we already had an infection peak recently.

It came during the summer and early fall, and was due to a new gang of variants known collectively as the FLiRTs for the pattern of their mutations. The immunity gained during that wave, plus Colorado’s continued better-than-the-national-average vaccine coverage, could be doing a lot to throw a blanket over what is normally a hot time for COVID transmission, said Dr. Rachel Herlihy, the state epidemiologist with the Colorado Department of Public Health and Environment.

“That is probably playing a role here, as is the underlying immunity of the population. As is the timing of the emergence of new variants,” Herlihy said. “So I think all of that, together, contributes to why we see surges when we see surges.”

But, as Herlihy indicates, there may also be deeper changes taking place.

Are hospitalizations a has-been?

Epidemiologists are evolving in the data they look at to track COVID.

Experts long ago stopped paying close attention to reports of new COVID infections. At-home testing means that most people aren’t reporting when they get sick with COVID, so infection data has become less reliable. That trend also threw off test positivity — looking at the percentage of COVID tests that come back positive.

So hospitalizations became a more important metric for watching COVID infection trends. People may not report when they’re sick, but they’re more likely to go to the hospital when they need to.  

But Herlihy said a larger number of people in the population with at least some prior COVID exposure or vaccination means that hospitalizations for COVID are now less likely. That can make hospitalization data less sensitive.

“It can be more difficult to see a clear trend with hospitalizations, especially when we are starting to see increases,” she said.

The proof is in the poop

Herlihy said it’s become much more important to watch multiple data sources to figure out what’s happening with COVID.

Testing on wastewater is now an early-warning system for COVID surges as well as those from other viruses. Data from emergency room visits has become more valuable, similar to how it is used to track flu.

The Centers for Disease Control and Prevention now produces simple updates based on measures of whether a virus’s infections are increasing, decreasing or staying flat. Its latest forecast shows COVID trends flat in Colorado, something that state wastewater and emergency room data seem to confirm.

The story is different for flu, though. Both CDC and state data seem to indicate that a flu surge is coming in Colorado.

“Once we start to see a gradual increase in flu, it usually takes off a few weeks later,” Herlihy said.

That’s a reminder that miserable viruses still abound this time of year, even if COVID may not be quite as abundant as it had been in previous years. Herlihy said vaccinations for flu, COVID and RSV are all still available for those who haven’t received one.