More than 2 million Coloradans have been fully vaccinated, Gov. Jared Polis’ office announced Thursday morning, shortly before state health officials expressed some cautious optimism about the state of the pandemic.

The 2 million fully vaccinated residents amounts to 43.8% of the eligible population, Kate McIntire, the deputy director of the state’s vaccine equity task force, told reporters. More than 2.6 million have received at least one dose, which is just over 57% of all Coloradans older than 15 years old.

In a statement, Polis congratulated “every Coloradan who has received their vaccine” and he urged those who haven’t to “make a plan today, and take the first step toward ending this pandemic and protecting your family.”

“Vaccinated Coloradans are experiencing the joy of safely seeing their grandparents again, or finally getting together with friends for dinner without the fear or guilt of endangering their lives,” Polis wrote. “There are even brighter days ahead Colorado, and this lifesaving vaccine is going to get us there.”

The impact of steadily increasing vaccination levels can be seen on the ground, said Rachel Herlihy, the state’s epidemiologist.

As she has said before, she stressed the parts of the state with high levels of vaccine uptake have low infection rates, and the opposite is true for those with low vaccination rates. Herlihy said there were roughly 30 cases per 100,000 people among unvaccinated Coloradans vs. 10.7 cases for partially vaccinated and just 2.3 cases for the fully inoculated.

The vaccine has been found to be 92% effective in Colorado, she said.

Overall, the state has seen “just a couple of days” of decreasing COVID numbers, Herlihy said.

According to data published daily by the state Department of Public Health and Environment, the seven-day average of new COVID cases has fallen from 1,711 on April 27 to 1,385 on Monday. The average positivity rate, which had hovered near a recent high of 6% for two weeks, has fallen to 5.6% since the beginning of May. 

But Herlihy urged caution in declaring an end to this fourth epidemic wave.

“It’s still too soon for us to know if that’s going to be a lasting trend,” she said. “We continue to see a high level of disease transmission occurring in this state, probably a high plateau.” 

The age group experiencing the sharpest increase in cases, Herlihy said, is 11- to 17-year-ollds. While the 18-and-older group has stabilized, the younger cohort has seen a steady increase in cases of late. What’s more, outbreaks among K-12 schools continue to climb week over week.

More than 2,000 students have been infected in school-based outbreaks in 2021, and outbreaks in schools have grown by more than 20% in each of the last two weeks. Last week, Polis said that could partially be explained by vaccinated adults taking their unvaccinated children to social events.

Herlihy on Thursday said part of the reason why the adolescent age group stands out is because older Coloradans are increasingly getting vaccinated, which in turn can cause other age groups to make larger shares of the overall infection rate.

The average age of Coloradans hospitalized with COVID, for instance, has dropped from 65 in the fall to 54 now.

“We probably would be seeing much broader transmission in different age groups if we didn’t have the vaccine available right now …,” she said. “Absolutely I believe that part of the reason we are seeing more transmission in younger populations is because our older populations are more highly vaccinated and protected right now.”

Federal regulators and health officials are expected to clear the Pfizer vaccine for use in those between the ages of 12 and 15 in the coming days. The drugmaker is expected to request approval for the 2-to-11 age group in September, CNN reported this week.

Though full vaccinations surpassed 2 million in Colorado, McIntire noted that vaccination administration has declined recently despite the state making every resident older than 15 eligible a month ago.

McIntire said “even though we’re seeing some decrease in uptake … we are still seeing a lot of folks being vaccinated and our numbers are still pushing up.”