Colorado’s latest COVID wave appears to have peaked, but new XBB.1.5 variant may be on the way

Colorado’s latest COVID-19 wave appears to have peaked, but the amount of respiratory disease in the state remains high, and it’s not clear if a new variant could change the trend.

The Colorado Department of Public Health and Environment reported 281 people were hospitalized with COVID-19 as of Tuesday afternoon, down from 306 a week earlier. Other measures also suggested that the virus was spreading less widely than it was a few weeks ago.

The state also got good news on respiratory syncytial virus, or RSV, which caused unprecedented hospitalizations among children in November. This week, RSV hospitalizations hit the lowest point in months, with 13 children and three adults admitted with the virus in the week ending Saturday. Since October, 2,268 people have been hospitalized with RSV in the Denver area.

The flu hospitalization rate also dropped in Colorado for a second week, but the trajectory wasn’t as clear, since the rate has see-sawed in recent weeks. So far, Colorado has recorded 2,468 flu hospitalizations, including 370 in the last week.

The percentage of emergency room and primary care visits for flu-like illness also dropped for two weeks, though the percentage of flu tests coming back positive remains high.

“To my eyes, it looks like it’s going down … but it’s not plunging,” said Beth Carlton, an associate professor of environmental and occupational health at the Colorado School of Public Health. “There’s still very high flu activity.”

Even though flu and COVID-19 appear to be in retreat in Colorado, it’s important to be up-to-date on your vaccines against both, Carlton said. People will still get infected, and some will become seriously ill before the respiratory season is over, she said.

“Even though both may have peaked in Colorado, there’s a long way to go,” she said.

The Centers for Disease Control and Prevention reported flu activity is declining nationwide, and estimated that 210,000 people have been hospitalized and 13,000 have died. While that’s a significant toll, it would be a relatively light flu season, assuming there isn’t another spike this winter.

The national picture is less reassuring for COVID-19. Hospitalizations topped the summer 2022 peak and are approaching April 2021 levels, with most of the growth in the eastern half of the country. Officials in New York, Boston and Los Angeles have asked — but not required — residents to wear masks again.

It’s not clear if that reflects seasonal factors — Colorado’s COVID-19 waves have tended to peak in November or early December, with the country as a whole following in January — or if it has more to do with the rise of a new variant, called XBB.1.5, Carlton said.

Like the other alphabet soup variants currently circulating, XBB.1.5 is in the omicron family. So far, there’s no indication that it’s more severe than other versions, though it does appear to be better at evading the immune system, she said.

“The question is if there is enough immune escape to see a rise” in cases and hospitalizations again, she said. “In a week or two, we should know more.”

The XBB.1.5 variant is taking over rapidly nationwide, rising from about 10% of cases in the week ending Dec. 17 to 41% in the week ending Dec. 31, according to CDC estimates. In New England, three-quarters of current infections are believed to involve XBB.1.5, as are more than 70% of cases in the region including New York and New Jersey.

In the region that includes Colorado, BQ.1.1 still accounts for just over half of infections, and XBB.1.5 is only responsible for about 2%, according to the CDC’s estimates. BQ.1.1 and XBB.1.5 both are resistant to antibody-based drugs, though antivirals like Paxlovid and remdesivir still work well.

At the moment, Colorado’s COVID-19 data suggests the situation is getting slightly better. Virus concentrations in wastewater were increasing in 14 utilities, declining in 18 and flat in 23.