Colorado’s school-aged children are experiencing the highest rates of coronavirus infection among any age group in the state right now.

But state health officials on Sept. 23 presented new data showing that requiring kids to wear masks while in school is associated with lower rates of COVID-19.

The data back up guidance from the Colorado Department of Public Health and Environment recommending that all schools implement universal masking policies for students, staff and visitors, regardless of vaccination status.

“The lower case rates are associated with districts that are requiring masks in schools, again showing a clear impact that masks are having in decreasing transmission in our school settings,” Dr. Rachel Herlihy, the state epidemiologist, said during a briefing with reporters.

Communities with higher rates of vaccination among school-aged children also have lower rates of coronavirus infection, according to CDPHE data.

You’ve heard over and over that this is now a pandemic of the unvaccinated. Well, a huge chunk of the unvaccinated statewide are kids — either those too young to be eligible for vaccination or those who are eligible but haven’t gotten the shot.

Since school started in mid-to-late August, Colorado kids ages 6 to 11 and ages 12 to 17 have had the highest coronavirus case rates in the state. For 12-17 year olds, an age group where kids are eligible for vaccination, infection rates rival the peaks of last winter.

For 6 to 11 year olds, who are not yet eligible for vaccination, these are the highest infection rates they’ve seen during the pandemic. Parents of kids in this age group received likely welcome news this week when the drug company Pfizer announced promising results in its tests of the vaccine for children ages 5 to 11 and indicated it would soon seek authorization for the vaccine to be administered widely.

Kids who are generally not yet school age, those up to age 5, have the lowest infection rates in the state.

The picture looks a little different at the local level in Colorado’s largest counties. Some counties have infection rates among school-aged kids that are more than double the infections rates in others.

Among the state’s 10 largest counties, Weld County has the highest rates for kids ages 6 to 17. El Paso and Larimer counties follow closely behind. On the lower end are Boulder and Denver, each with case rates among school-aged kids that are less than half of Weld County’s.

One of the big points that state health officials hoped to get across during the Sept. 23 briefing is the importance of getting vaccinated. Counties with higher vaccination rates among school-aged kids are generally the ones with lower case rates.

Weld County, for instance, has the second-lowest vaccination rate for kids ages 12 to 17 among the state’s 10 biggest counties — around 40%. Boulder, which has a vaccination rate around 70% for kids 12 to 17 has the second-lowest case rate.

“We see this clear correlation between high vaccination rates and low case rates, and that’s true not just for the adult population but also holding true for our children,” Herlihy said. “So this could certainly be one reason that we are seeing differences in pediatric rates across the state right now.”

Lastly, CPDHE looked at age-adjusted case rates for kids in 48 school districts, split into two groups by whether the districts are requiring masks in schools.

Case rates among the two groups tracked pretty closely until late-August, around the time when school started. Rates increased for both groups after that, but with a twist: Districts not requiring masks saw faster growth in cases and hit a higher peak than districts requiring masks.

By mid-September, case rates in the non-masking districts were significantly higher — about 20% higher — than the rates in the districts with masks policies.More than three-quarters of Colorado kids now attend school in a district that has a mask mandate.

This story is from The Colorado Sun, a journalist-owned news outlet based in Denver and covering the state. For more, and to support The Colorado Sun, visit coloradosun.com. The Colorado Sun is a partner in the Colorado News Conservancy, owner of Colorado Community Media.