Under the state's current vaccination trajectory, two-thirds of Coloradans over the age of 11 will be at least partially inoculated by Labor Day, according to new projections released by state health experts Thursday.

The report, which has been released intermittently over the past year by researchers at the Colorado School of Public Health, provides one of the rosiest projections of the coronavirus's presence in months. The researchers estimate that one in 390 Coloradans are infectious, far fewer than the one-in-81 figure included in the May modeling report and an improvement on the projections from March, which were similarly optimistic. What's more, roughly 54% of the state was believed to be immune to the virus, through a mix of vaccinations and prior infections.

Those levels of immunity vary widely across age ranges, according to the team's projections. Those estimates dovetail with the state's vaccination rates, which are high among older residents and steadily drop from there. Three-quarters of Coloradans 65 and older are immune, according to the report. That drops to 64% for those between the ages of 40 and 64, then declines further to 56% between 20- and 39-year-old residents.

The smallest share is among those under the age of 20: Just 25% of those Coloradans are immune. That number, though, is more complicated than others. For one, only half of that age group are even eligible to be vaccinated; those under the age of 12 are still not able to get vaccinated, and those between the ages of 12 and 15 have only been eligible since May 10.

The vaccination rates do not just differ across age groups. Overall, 3.26 million Coloradans have received at least one vaccination, while just under 3 million are fully inoculated. But rates vary widely across counties. Thirteen counties, led by San Miguel's 93.6%, have given at least one inoculation to more than 70% of their eligible residents. But 27 counties have been unable to do give one dose to at least 50% of their population; more than a fifth of the state's total counties are below 40%.

The disparate rates lead to more infections, more hospitalizations and more deaths than in low-uptake areas.

"The course of the pandemic varies across the state," the researchers wrote. "Areas with higher vaccination rates are seeing fewer SARS-CoV-2 cases, hospitalizations, and deaths. Areas where infection prevalence is high and/or infections are flat or increasing are regions with some of the lowest vaccine uptake rates in the state."

That dynamic has been exacerbated by the rise of the delta variant, which now accounts for the majority of the COVID-19 cases in Colorado, according to state data. The modeling team wrote in its report that the variant, which was first identified in India, is both more infectious and and can "modestly" weaken the strength of vaccines, even when compared to another previously dominant variant. 

"Infection with the Delta variant leads to 10% more breakthrough infections among the vaccinated," the modelers wrote. A breakthrough infection occurs when a vaccinated individual contracts COVID-19. "Both the CDC and Public Health England have stated that it is likely that vaccines confer modestly less protection against symptomatic infection with the Delta variant. The Delta variant has grown rapidly in Colorado, and currently accounts for over 75% of infections."

The effects of the delta variant, coupled with low vaccination rates, are plaguing Mesa County. As of Thursday afternoon, 45% of the county's residents had received at least one dose. According to Mesa County Public Health's website, 99.2% of all hospital beds in the county are currently occupied, plus nearly 96% of staffed intensive care beds. Nearly 60% of ventilators are also currently in use.

The one-week cumulative incidence rate in Mesa County is nearly 10 times that of Denver, according to data published by both counties' health departments, despite Mesa having fewer than a quarter of the capital county's population.

Jon Samet, the dean of the public health school, said in an email late last week that the state has "work to do to increase the vaccination rate."

"We will be left with a patchwork of more and less protected regions, setting up for flare-ups in parts of the state, e.g., Mesa County at the moment," he wrote. "These counties are targeted with initiatives, but not enough progress (has been made)."

Still, despite the disparate vaccination rates, Samet and his team's latest model is far more positive than many of their previous reports, which they had often used to sound the alarm about the risk of spiking case numbers and hospitalizations should the state slip.  

Colorado has averaged just under 320 new cases per day over the past week, a number that's held relatively stable since mid-June and is down more than 80% since late April. Hospitalizations have also fallen, but that number has proven more stubborn to push down: Though they fell from 731 total confirmed and suspected COVID-19 inpatients on May 8 to 302 on June 27, they crawled upward again and now stand at 350.

Health reporter

Seth Klamann is the health reporter for the Gazette, focused on COVID-19, public health and substance use. He's a Kansas City native and a University of Missouri alum, with stops in Wyoming, Omaha and Milwaukee before moving to Denver.

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