The omicron variant is expected to be Colorado’s dominant strain of the novel coronavirus in the coming days and weeks, state and local officials said Tuesday, and its presence has likely led to a surge of cases in Eagle County.

Omicron accounted for more than 9.7% of positive COVID-19 cases in Colorado last week, according to state data, up from 1.22% the week before.

Over that same time period, it has become the dominant strain nationwide. Community transmission has been detected in Denver and elsewhere in Colorado.

“At this point, we can essentially confirm that transmission of omicron variant in Colorado is occurring,” Gov. Jared Polis said Tuesday. “It still is not the predominant strain in Colorado, but based on what has occurred elsewhere, we expect omicron to increase even as we continue to see delta to decrease, which is what we’ve been seeing the last few weeks.”

“Like we’ve seen in other parts of the country, we anticipate omicron will become the dominant variant in Denver very soon,” said Tori Burket, the epidemiology and disease intervention manager for the Denver Department of Public Health and Environment. “Early data indicate that the omicron variant is more contagious than the delta variant, and we anticipate case rates to increase as we know community transmission is occurring in Denver and in the state.”

Polis said omicron was beginning to spread in parts of the state with high levels of travel, ticking off Eagle, Summit and Pitkin counties. Eagle has seen its cases surge over the past week: It averaged about 15 cases per day on Dec. 12. But that average has nearly tripled in the days since, to more than 43 cases per day by Sunday. The county reported 139 new cases Monday, the most it has identified in a single day during the pandemic, according to the Eagle County Public Health website.

A spokesperson for the state Department of Public Health and Environment said Monday that “sequencing is pending” to confirm omicron is driving the spread in Eagle County. But the area’s samples contain a telltale marker that indicates the presence of the new variant, the spokesperson and Polis said this week.

“That plus their rapid rise suggests it is highly likely that omicron is circulating there,” the spokesperson said in an email Monday night. A follow-up email sent Tuesday morning to the state health agency was not returned.

Attempts to reach public health officials in the county were unsuccessful Tuesday. On Friday, Eagle County Public Health issued a public health advisory warning of the “sharp increase in cases.”

“This is an indication that community spread is very high and the likelihood for exposure has increased considerably,” the agency wrote. “In addition, local testing is quickly reaching its capacity and persons with symptoms will be prioritized for testing.”

Omicron was only officially identified a month ago but has surged to become the dominant variant in the United States. The Centers for Disease Control and Prevention said Monday that the latest strain accounted for 73% of cases in the country over the past week.

In Colorado, the variant has been identified in several counties, including Denver, Arapahoe, Jefferson, Boulder, Pitkin, El Paso and Garfield. The cases in Denver and Garfield counties have been linked to community transmission, as opposed to infections picked up while traveling. Wastewater sampling has also indicated traces of the variant in various systems around the metro area.

In addition to two cases related to community transmission, Denver officials have identified a third case in the county, tied to an outbreak in Chicago. Burket, of the Denver health department, said that given omicron’s high level of transmissibility, “we do anticipate there are other omicron cases that have not yet been sequenced or reported.” She emphasized the need for boosters as a key method in combating the new strain’s spread and blunting its impact for those infected.

Though omicron is now widely considered to be more transmissible than other strains of the virus, it remains unclear if it’s more severe. The impact of omicron on Colorado will in part hinge on that question, experts said.

“Omicron is here for sure with last week’s surge in Eagle County probably a signal,” said Jon Samet, dean of the Colorado School of Public Health. “The good news is that omicron will arrive while delta is descending, easing the strain on the medical care system. From what we know in other countries, omicron will likely rise steeply because of its transmissibility and immune escape. The impact on health care and on Coloradans will depend on its virulence.”

The variant’s arrival here comes as the state emerges from a prolonged COVID-19 surge that threatened to overwhelm hospital capacity and caused mortality levels to spike to their highest point in a year. But Colorado appears to have avoided that worst-case scenario: Though hospital bed capacity remains limited, COVID-19’s direct burden on hospitals has lessened of late. There were 1,030 people hospitalized with the disease here as of Tuesday afternoon, a sharp decline from 1,565 on Nov. 22.

Polis said Tuesday that the use of monoclonal antibodies — which can help prevent severe disease if given early — helped avoid hundreds of hospitalizations and dozens of deaths.

With many questions still to be answered about omicron, it remains unclear how it will impact Colorado’s people, hospitals and day-to-day life as it gains ground. Polis said the state was watching other parts of the country and world that are dealing with new surges.

Much of that information is concerning. Glen Mays, also of the public health school, said in an email that “there is a real possibility of a new surge in infections and hospitalizations due to omicron.”

“We still have large pockets of susceptible people across the state, and omicron appears much more transmissible than other variants,” he said. “High risk adults who have not yet received a booster vaccine are of particular concern. Long-term care facilities and other congregate care institutions are again areas of concern.”

Polis told reporters Tuesday that a third vaccine dose — or second, if you received Johnson & Johnson initially — should no longer be considered “optional” and that it should instead be viewed as part of the normal course of full inoculation. Mays said vaccines and boosters will continue to offer protection against omicron going forward.

Samet agreed.

“The goal is to avoid severe COVID-19 and death,” he said. “We have that possibility with vaccination, including a third dose. With that third dose for the mRNA vaccines, there is strong protection against hospitalization and death.”