Four Corners Public Radio | By Olivia Prentzel, John Ingold, and Michael Booth/The Colorado Sun

Published August 20, 2021 at 6:27 PM MDT

Mark Duggan
San Juan County, Colorado, home to the town of Silverton, has 81% of residents vaccinated. But more than 29 cases of COVID were reported in the past month.

This story originally appeared in the Colorado Sun.

In the fight against the coronavirus, Pitkin County has a lot going for it.

The county, home to well-heeled Aspen, has one of the highest vaccination rates in the state. Among all its residents, of any age, 63% are fully immunized.

So, when the county’s coronavirus infection rates soared in recent weeks, health officials in the county wondered why that high level of vaccination didn’t appear to provide better protection. In investigating, they hit on one possible reason that leaders in other mountain communities have noticed too: It’s the tourists. In a Colorado resort town, your community is only as protected as your visitors are.

“The vaccination rates from the positive cases of the tourists that are coming are lower than our overall rate (among residents),” Kurt Dahl, Pitkin County’s environmental health manager, said. “I think that’s one of the thoughts or ideas: Are we diluting our own rates?”

In some of Colorado’s most-vaccinated counties, unvaccinated visitors appear to be confounding efforts to keep COVID-19 out.

About 66% of the COVID-19 cases reported in the past month in Pitkin County are breakthrough cases, or those involving vaccinated people, according to public health officials. Despite the county’s vaccination rate among residents, cases continue to rise, possibly due to unvaccinated tourists, Dahl said.

In the past 14 days, at least 38% of positive cases reported in the county were among its visitors, Joshua Vance, one of the county’s epidemiologists, said during an Aug. 12 Board of Health meeting.

“This rate has remained very consistent for the past month, where we have seen a very high rate of visitors that are here in Pitkin County and testing positive,” Vance said.

Visitors to the county are much less likely to be vaccinated, Vance said, based on data from contact tracing. Of those who tested positive in the past month, 66% of residents were vaccinated, whereas only 42% of visitors were immunized.

“This underscores the fact that we are seeing a dilution of our vaccination rate when individuals are coming here and they are not fully vaccinated,” Vance said.

It’s still unclear why the county is seeing higher rates of breakthrough cases than expected and determining an exact cause with such small numbers is hard, Dahl said. His team is also looking to see if another variant — one that’s more resistant to vaccines — is circulating in Pitkin County.

On Monday, Pitkin County’s public health officials met with the Colorado Department Public Health and Environment to discuss the trend, Dahl said.

“We agreed to monitor this and if the trend continues, we will be back with CDPHE,” Dahl said. “To draw conclusions at this point, it doesn’t make sense. We know the vaccines are working.”

Breaking down breakthrough cases

Across the state, breakthrough cases remain relatively small. Between January to Aug. 10, there have been 10,342 breakthrough cases in Colorado, accounting for 4.6% of all cases during that time period, according to CDPHE.

Looking over just the past couple of months, breakthrough cases statewide have made up a higher percentage — about 20% of cases. That may partly be due to the supercharged infectiousness of the delta variant, but it is also to be expected. As vaccination rates rise and the pool of unvaccinated people shrinks, breakthrough cases will make up a higher proportion of all cases.

Mark Duggan
Summit County’s Lake Dillon in an early winter scene, with I-70 in the foreground. The county’s population skyrockets from 31,000 to as much as 72,000 during high-visitation seasons.

Public health officials in Summit County, where 72% of its residents have been vaccinated, share the concern that its visitors are increasing risk. The county, which is home to several mountain communities including Breckenridge, Silverthorne and Dillon, can see its population skyrocket from 31,000 to 72,000 on any given day during high-visitation seasons, said Wesley Black, the county’s branch chief of COVID-19 contact tracing team.

“Summit is definitely proud to be the travel destination for so many folks and we love them to come and experience the beautiful place that we call home,” Black said.

That being said, Black warned that with more visitors comes the increased risk of spreading disease.

“Residents and visitors, we all really want to just enjoy the festivals, the concerts, shops and restaurants that Summit has to offer,” Black said, “and it can be done safely if the right precautions are taken, of course.”

The county saw a “pretty significant increase” of breakthrough cases in July, though those were coupled with a spike in overall cases, Black said. About one-third of the positive cases are among those who are vaccinated.

While the county doesn’t have data to show how many unvaccinated people have visited the county, Black said the contact tracing team has communicated with visitors who live across the U.S. and abroad.

“The more people you throw into the mix, the more complicated things get,” Black said.

Last week, the county identified outbreaks at two restaurants, which in total infected 11 employees — some of whom were vaccinated and some of whom were not, Black said.

Black stressed the importance of getting tested after experiencing symptoms that could be related to COVID-19. Several of the employees from the latest outbreaks reported they worked while experiencing symptoms, he said.

“Don’t chalk it up to allergies from the flora that is blooming or the smoke in the atmosphere right now because you can’t really rule out COVID until you get a test that is negative,” he said.

The county has required all students, teachers and visitors to wear a mask at school, which began Wednesday. As of Monday, all visitors to county facilities will need to wear a mask regardless of their vaccination status.

Vaccinating the visitors

La Plata and Archuleta counties — home to Durango and Pagosa Springs, respectively — were one of the vaccine campaign’s early success stories, with lightning-fast distribution that led to state-leading immunization rates. When the counties began seeing cases surge this summer, it wasn’t exactly surprising to Liane Jollon, the executive director of San Juan Basin Public Health, which covers both counties. The delta variant was first identified in Colorado on the Western Slope, and Jollon had been prepared for its arrival in southwest Colorado.

Still, as cases rose, she suspected something else was also at work.

“We are seeing across Colorado a faster-rising rate in our resort, high-visitorship communities,” she said. “And we expect that’s due to an influx of individuals and a high turnover of individuals.”

About 30% of the counties’ cases have been in vaccinated people over the past month. But the vaccines continue to be highly effective at preventing severe illness. Unvaccinated or partially vaccinated people account for 90% of hospitalizations over the last month, said Chandler Griffin, a spokesman for San Juan Basin Public Health.

Jollon said the agency conducts full case investigations and contact tracing for all coronavirus infections in visitors. Griffin said in the last month, visitors have accounted for about 15% of all cases.

It has also extended its vaccination outreach to visitors. People arriving at the Durango airport see signs encouraging them to get vaccinated, and San Juan Basin Public Health said out-of-towners are welcome at the communities’ vaccination clinics.

“If someone wants to get vaccinated, we want them to very easily be able to find a clinic,” Griffin said. “Immunity for someone protects the rest of the community.”

Mark Duggan
A March 2021 vaccine clinic in Durango.

Not even the most-vaccinated county in Colorado has been spared. According to state data, 81% of residents in tiny San Juan County — in southwest Colorado — are fully vaccinated. But, last week, public health officials in the county, home to Silverton, issued an indoor mask mandate, regardless of the person’s vaccination status.

After seeing a total of only 47 COVID-19 cases through Aug. 3, 29 cases were reported between then and Aug. 11. That put the county’s risk of spread at “very high” according to state guidelines.

As of Tuesday, two residents remain hospitalized due to COVID-19, the county’s office of emergency management said in an email.

“Although San Juan County has a high community vaccination rate, several factors have influenced the increase in cases which include a fluctuating summer seasonal worker population, recent indoor events, unvaccinated residents, and a surge of unvaccinated visitors,” the county public health department wrote in a news release posed to Facebook on Tuesday.

San Juan County Public Health director Becky Joyce urged residents to get vaccinated, calling the hospitalizations of two residents a “wakeup call.” She asked the community to be “flexible” and “part of the solution” during the new outbreak. Masks are not required in any outdoor setting in San Juan County.

“The majority of the positive COVID-19 cases are in unvaccinated people undeniably,” Joyce said in a statement, “and knowing that two of our locals are currently hospitalized due to COVID-19 is a wakeup call for our community.”

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This story was written in partnership with the Colorado Sun, through a collaboration powered by COLab, the Colorado News Collaborative — a nonprofit formed to strengthen local public-service journalism in Colorado. KSUT joined this historic collaboration with more than 40 news organizations to share in-depth local reporting to better serve Coloradans.

Mark Duggan provided online production of this story for KSUT.