Colorado sees summer COVID bump as new FLiRT variants keep virus from settling into seasonal pattern

Colorado, along with much of the country, is experiencing a summer bump in COVID-19 infections, showing the virus has yet to fall into a seasonal pattern.

Flu, respiratory syncytial virus and other common respiratory bugs typically start spreading in the fall and peter out by spring. In Colorado, the worst points of the pandemic fell in the fall and winter, but COVID-19 hasn’t disappeared in the warmer months, as flu does.

Four years ago, at the beginning of the pandemic, scientists expected the virus would be well on its way to settling into a seasonal pattern by now, said Talia Quandelacy, an assistant professor of epidemiology at the Colorado School of Public Health.

Now, they’re less sure whether COVID-19 will eventually do that, or if it can keep churning out new variants fast enough to remain active year-round, she said.

“That’s one of the big questions in the field,” she said.

Colorado’s most recent weekly wastewater data showed concentrations of the virus increasing in three-quarters of the 55 utilities statewide that supplied information. The state’s wastewater data doesn’t indicate how widespread a virus is, but it can show whether that particular infection is becoming more or less common.

The number of Colorado watersheds showing an increasing pattern has gradually risen since early May, when none were.

The number of new COVID-19 cases reported to the state also has trended upward since mid-May, though since relatively few people get tested in facilities that report results, the figure isn’t a reliable indicator of how many Coloradans actually got sick.

Nationwide, the percentage of tests coming back positive, emergency department visits for the virus and COVID-19 deaths all have risen in recent weeks, Quandelacy said.

Hospitalizations ticked up nationwide, rising about 36% from their low point in May, before flattening in early June. They remain low, however, with about 1.5 COVID-19 hospitalizations for every 100,000 people, compared to a rate of 7.7 per 100,000 people last winter. The Centers for Disease Control and Prevention no longer requires all hospitals to disclose how many COVID-19 patients they’re treating, and only about one-third do voluntarily, making the number of patients significantly fuzzier than it was earlier in the pandemic.

Data on the percentage of tests coming back positive, prevalence in wastewater and emergency room visits also indicate whether the virus is becoming more or less common, but don’t allow for exact comparisons to previous years.

Unlike in some previous waves, this one isn’t the result of one variant gaining dominance, Quandelacy said. Rather, KP.3, KP.2 and LB.1 combined have dethroned JN.1, which dominated during the winter and early spring. All are descendants of omicron and appear to be about equally likely to cause severe illness. Some epidemiologists group the three together under the term “FLiRT” variants, based on a shortening of the technical terms for their mutations.

“I think it does have to do with these new variants,” she said. “Having all of these circulating together means we’re more likely to have infections.”

In Colorado, rates of COVID-19 remain low, with 87 people hospitalized with the virus statewide as of Tuesday, though infections have increased slightly in recent weeks, said Kayla Glad, spokeswoman for the Colorado Department of Public Health and Environment.

At the low point at the end of April, 75 people were in Colorado hospitals for the virus. The shifting variants could be a factor, but other possibilities include summer travel, people spending more time indoors as the weather heats up and waning immunity, she said.

Also, most people haven’t had a COVID-19 vaccine in a year or longer, Quandelacy said. While protection against severe illness lasts longer, immunity to infection starts to wane within months.

People who didn’t get boosters in the fall or winter should consider one now, particularly if they are at higher risk of severe illness, Quandelacy said. The Centers for Disease Control and Prevention recommended that everyone six months and older receive the latest COVID-19 shot when it becomes available, but that won’t be for at least another three months, she said.