A Colorado city is 99.99% vaccinated. COVID is not over there.

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San Juan County, Colorado – with a single incorporated city of Silverton (pictured) – is one of the most vaccinated counties in the United States.

San Juan County, Colorado, boasts that 99.9% of the eligible population has received at least one dose of COVID-19 vaccine, placing it in the top 10 counties in the country, according to data from the Centers for Disease Control and Prevention.

If vaccines were the only armor against COVID proliferation, San Juan County on paper with its approximately 730 inhabitants on paper would be one of the safest places in the country.

Yet the last few months have shown the complexity of this phase of the pandemic. Even in an extremely vaccinated place, the shoots alone are not enough because geographical boundaries are porous, vaccine effectiveness can decline over time, and the Delta variant is highly contagious. Experts in infectious diseases say that masks are still needed to control the spread of the virus.

The county registered its first hospital admissions of the pandemic in early August – this year, not 2020. Five summer residents were admitted. Three ended up on fans: Two recovered and the third, a 53-year-old woman, died in late August. All are thought to be unvaccinated.

These cases, and even those that did not require hospitalization, gave alarm to the county with a single built-up town: Silverton. It is a densely populated former mining community located in the mountains of southwestern Colorado, where snowstorms and avalanches often block the lonely road that passes through.

“The pandemic is just continuing,” said DeAnne Gallegos, the county’s public information officer and director of the local chamber of commerce. “We always thought it was going to end before this summer. Then we thought in November. Now we say, ‘No, we do not know when.'”

So the county decided to go back: “We went back to the tools that we knew we had,” Gallegos said. “Mask mandate indoors and then counteract indoor events.” Outdoor events continued, such as a brass concert on the courthouse steps and the area’s signature Hardrockers Holidays mining competition with its pneumatic mucking and spike driving.

In all, 85% of the county’s total population is fully vaccinated when sets under 12 are taken into account. But in the summer, the population almost doubles as seasonal residents sleep in second homes and RV parks, some taking vacations while others take seasonal jobs. Then there’s what Gallegos described as the “tourism tsunami” – the daily influx of people arriving at the historic railroad from Durango and the dusty jeep trails through the mountains. Many of these visitors have unknown vaccination status.

The county’s 2-week incidence shot up in August to the highest rate in the state and remained there for most of the month. Although this increase amounted to a total of about 40 known cases, it was almost as many as the county had logged during the entire pandemic – and cases also spilled into the vaccinated.

Any number of cases would be a big deal in a small place without its own hospital. “We’re all one-man bands just trying to make it happen,” Gallegos said. The county’s public health director, Becky Joyce, for example, does everything from contact tracking and COVID testing to firing. And when the county restarted its mask mandate, it was Gallegos who designed the signs and spent his weekend tying them around town.

The largest concentration of COVID cases occurred at a motorhome park and a music festival run indoors by rain.

“It makes sense that people who came out of 3 or 4 weeks of just blocking tourism started getting sick working in the restaurants at the RV parks,” Gallegos said. “And then you gather all the locals condensed together for a couple of nights of concerts, and that was just trifecta.”

Dana Chambers, who runs the hardware store in Silverton, was vaccinated as soon as possible. She said returning to a mask mandate in some ways felt like “a step back”. But she said companies like hers need summer tourism to survive the quiet winter when just a few hundred tourists arrive, largely to jump out of helicopters on ski terrain. “If we have to wear the mask, that’s what we do.”

Julia Raifman, a Boston University School of Public Health epidemiologist who follows the state’s pandemic policy, is not surprised that COVID can attack a place like San Juan County despite high vaccination rates.

Data show that the vaccines protect against death and hospitalization due to COVID. But even effective vaccines do not match Delta’s transmissibility. “Even at best — if vaccines reduce transmission by 80% —you’re actually twice as likely to get COVID now than you were in July,” Raifman said because of the virus’ recent spread. “It is statistically impossible to obtain herd immunity with the Delta variant.”

Meanwhile, many local and national leaders, including in Colorado, continue to focus on vaccines almost exclusively as the way forward.

Talia Quandelacy, an epidemiologist at the University of Colorado-Denver and the Colorado School of Public Health, said the concept of herd immunity in this pandemic has become simplified and over-dependent. “It’s a useful guide to having some kind of goal to aim for,” she said. “But usually, if we hit a particular measurement, it does not mean that transmission or the pandemic will just go away.”

Many researchers agree that especially with most of the world still unvaccinated, COVID is probably here to stay and eventually turn into something more like the common cold. “It’s probably going to be a matter of a few years,” Quandelacy said. “But that seems to be the path we are on.”

For that reason, the “target language” used by many politicians has frustrated Anne Sosin, a politician at the Nelson A. Rockefeller Center for Public Policy at Dartmouth College who studies COVID and rural health. The vaccines do what they are supposed to do – prevent people from getting really sick, do not prevent them from ever becoming infected – but it has not been well communicated. “The messages surrounding this have not been very nuanced,” she said.

She pointed to the experience of an epidemiologist who wrote in August in The Baltimore Sun. that he had caught COVID at a house party where all 14 guests and the host were vaccinated. The host had infected him and nine others. “As miraculous as they are in keeping people out of the hospital and alive, we cannot trust them alone to prevent infection,” Sosin said of the vaccines.

And public health experts said San Juan County shows that measures like masks, ventilation and distance are also needed. They circulate the “Swiss cheese” model of COVID defense, where every precautionary measure (or layer of cheese) has holes in it, but when stacked together, they create an effective defense. Sosin said rural areas in particular may need these layers of defense because residents are often closely connected and diseases are moving rapidly within social networks.

Joyce, the director of public health, who declined an interview request, wrote on Facebook in August that the county’s recent experience proved “the vaccine creates a line of defense, but does not make us invincible to this disease or the variants.”

Raifman considers this realization – coupled with San Juan’s subsequent demands for indoor masks – as a success in a crucial moment. The month-long mandate was then lifted on September 10, when the county had fallen back to a low COVID transfer rate. At the time, it was the only county in Colorado with such low transmission.

“This is the moment where we define in a way: How do we deal with the virus in the long run?” Said Raifman. “So far, we define that we can’t handle it; we let it control us.”

Even after lifting its mask mandate, the Facebook page of the county’s public health department urges residents to wear masks and “be aware of the COVID-19 situation, just as you are aware of the weather.”

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