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LONE TREE, Colo. (KDVR) — COVID-19 continues to spread and mutate among unvaccinated people, furthering the rise of breakthrough cases among the vaccinated population, health experts say.

New data from Colorado Department of Public Health and Environment shows the percentage of COVID-19 cases reported in vaccinated individuals in Colorado is increasing.

Colorado reported that 21.9% of the cases logged in July were among vaccinated people. That percentage rose to 26.8% among the cases reported the week of Aug. 8-14.

“Certainly, more regionally there has been an increase in folks who have been vaccinated coming down with symptoms. Generally, they’re not as sick as people who are unvaccinated,” said Dr. Eric Lung, chief medical officer at Sky Ridge Medical Center.

Lung says a vast majority of the vaccinated patients they’ve seen admitted for COVID-19 have comorbidities and underlying health conditions.

“It’s folks who have hypertension, cardiac disease, respiratory issues or a history of cancer,” Lung said.

Unvaccinated people make up a vast majority of COVID-19 hospitalizations across the state. State data shows in July, 1,365 people were hospitalized with the virus. Unvaccinated people made up 88% of that population.

Lung says the increase in all infections is driven by the highly contagious delta variant.

“We need the people who are unvaccinated to get their first and second doses so that we don’t have a continued spread of any virus, so that it doesn’t continue to mutate. That’s really the key to ending this pandemic,” said Lung.