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As coronavirus cases rise again, not even Colorado’s most-vaccinated counties have been spared. Here’s why.

State and local health officials have had a mixed response to new federal guidance urging vaccinated people to start wearing masks again

A coronavirus piñata at a vaccine event in Henderson on Feb. 26, 2021. (Jesse Paul, The Colorado Sun)
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As you rub your neck from the public-health whiplash that occurred this week when federal officials recommended that many people vaccinated against the coronavirus go back to wearing masks, consider this dizzying detail:

Residents of some of the most-vaccinated counties in Colorado — the places that state officials have lauded as doing the best job in working to stop the virus — are now being urged to resume donning that most prominent of pandemic precautions. Residents of some of the least-vaccinated counties in Colorado are not.

This seemingly incongruous scenario is due to the pandemic taking yet another surprising turn in Colorado.

The new guidance from the Centers for Disease Control and Prevention recommends that people in areas with lots of new coronavirus cases resume wearing masks when around others indoors. The guidance puts the threshold for mask-wearing at 50 new cases per every 100,000 people over the previous week or at a test-positivity rate of at least 8%.

A month or two ago in Colorado, a county’s vaccination rate was a somewhat reliable predictor of what its coronavirus case rate would be. Counties with higher vaccination rates generally had lower case rates, and counties being hit hard with surges of infections — Mesa County was a frequently cited example — often had lower vaccination rates.

But since then, the fearsomely transmissible delta variant has exploded across the state. It is now believed to account for 95% of new cases in Colorado, having virtually squeezed out all competing variants. Around 685 new coronavirus infections are being reported a day in Colorado right now — numbers not seen since late-May, when the state was on the downward slope from its previous case surge. Hospitalizations are also ticking upward, though more slowly.

And the correlation between vaccination rate and case rate has broken down.

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On Thursday, 44 of the state’s 64 counties had case rates high enough to fall under the CDC’s masking guidance, according to state data. Those counties include 18 of the 20 most-vaccinated in the state. (The CDC’s map of counties in the mask zone has a different count in part because the agency is working with older data than the state is.)

The highest one-week case rate in the state on Thursday was in the third-most vaccinated county: Summit County, where more than 77% of the eligible population is fully vaccinated but which reported 287 new cases per 100,000 people over the past week, according to state figures. The fourth-highest case rate was in Mineral County, the fourth-highest vaccinated county.

Of the 20 least-vaccinated counties in Colorado, half of them Thursday reported one-week case rates low enough to exempt them from masking guidance. And, taking a longer view by looking at two-week cumulative case rates, the transmission trends are just as muddled. 

So, what exactly is going on here?

May Chu, an epidemiology professor and infectious disease expert at the Colorado School of Public Health, said one explanation involves the demographic characteristics of the least-vaccinated counties. Despite having a high percentage of people who are potentially susceptible to the virus, they’re not places where the virus can spread easily.

“Some of those are very rural counties where density is not a big issue,” she said.

Another possible explanation involves previous coronavirus case surges. Researchers at the Colorado School of Public Health have estimated that, while the Eastern Plains has some of Colorado’s least-vaccinated counties, it has some of the highest rates of immunity — due to a high percentage of people who have previously caught the coronavirus.

Lincoln County Public Health Director JoBeth Mills administers a coronavirus vaccine on March 19, 2021, in Hugo, Colorado. The vaccine event served 298 people, 60 of them from Lincoln County. (Brian Malone, Special to The Colorado Sun)

“Biology is messy”

But Chu said the CDC’s new guidance is also a natural result of researchers and health officials trying to understand a complex microbiology problem while simultaneously making recommendations to the public on how to stay safe. It feels whiplash-y because that’s sometimes how science works.

“There’s a lot of pressure as to what’s the right thing to do for COVID,” she said. “I always try to think of it this way: We’ve had the virus for about a year and a half. In terms of microbiology, this is a very, very young virus still, and there are a lot of things we don’t know about it.”

“This is biology,” she said. “Biology is messy.”

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In particular, the mask guidance comes after a startling new revelation about the delta variant. According to reporting by The Washington Post, federal authorities reviewed research suggesting that vaccinated people may be highly capable of spreading the variant if infected by it — perhaps just as capable as unvaccinated people. The data are expected to be released Friday.

Vaccination still appears effective at preventing people from getting really sick or dying, even if they are infected with the delta variant. But the new research has led to concerns that the previous CDC guidance — that vaccinated people can go maskless pretty much anywhere — could lead to yet another surge of the virus.

And, because there are still a lot of unvaccinated people and also a lot of people for whom the vaccine is less effective due to underlying health issues, a new surge could lead to many more deaths.

“If they’re not masked,” Chu said of vaccinated people, “then it’s just like February of last year.”

A masked installation by artists Darrell E. Ansted and Cynthia Allen outside of Molly’s Spirits in Lakeside on May 2, 2021. (Eric Lubbers, The Colorado Sun)

Local officials scramble to respond

But the CDC’s new guidance appears to have caught state and local health authorities off guard.

On Thursday, the Colorado Department of Public Health and Environment still had not said whether it endorses the guidance and will, likewise, recommend that people start wearing masks again.

Several county public health departments said they are still reviewing the guidance and had not made a decision on whether to recommend or re-mandate masks. Jefferson County Public Health issued a statement Thursday evening saying it “strongly encourages” residents to wear masks in public indoors settings, regardless of vaccination status.

“We know this is discouraging news, especially after months of progress,” the agency’s executive director, Dr. Dawn Comstock, said in a statement. “We don’t want to give up the ground our communities worked so hard to take during this battle against COVID-19. By taking recommended precautions now, we can work to minimize viral transmission to prevent the delta variant from spreading even further.”

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The public health board in Pitkin County — another highly vaccinated county with currently high case rates — plans to discuss at its next meeting whether to reissue a mask order.

Gov. Jared Polis on Thursday continued to portray the pandemic as a matter of personal responsibility — something that can be ended through individual action. His office sent out a news release stating that the coronavirus is “spreading in areas with low vaccination rates even though there is ample supply and access to the safe and effective vaccine.”

“This is now becoming a pandemic of the unvaccinated and we have the tool to end it,” Polis said in a statement. “Now more than ever it could not be more clear that you are either on the side of spreading this virus or you are on the side of helping the state get back to the Colorado we know and love.”

And, to be sure, vaccination remains a key way to fight back against the delta variant’s onslaught. Last week, Tri-County Health Department, which serves Adams, Arapahoe and Douglas counties, said that 95% of its coronavirus hospitalizations since March have been in people who were not fully vaccinated against the virus.

“Getting vaccinated against COVID-19 is the most effective way to protect yourself against this virus, especially with the more contagious delta variant circulating,” Dr. John Douglas, Tri-County’s executive director, said in a statement.

But over the past several months government leaders have often pitched vaccination as having another benefit: It allows you to return to your normal life; it allows you to take off your mask.

Chu said public health messaging through the pandemic has been imperfect. And she said the new U-turn on mask guidance should prompt a different approach: Tell people that masks are a valuable part of our lives now. They are here to stay, at least in some form.

Because, otherwise, we might be setting ourselves up for whiplash all over again.

“The virus itself is going to change,” she said. “This delta variant, when we get over it — and we will — is not going to be the last one.”


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