Boulder County identified its first case of the omicron variant Friday, county officials said, 24 hours after Colorado confirmed its first case.

The Boulder County man had recently traveled to South Africa, the county’s public health department said. The patient tested positive for COVID-19, and given their recent travel history, their sample was flagged for further investigation. The omicron case was confirmed by the state Department of Public Health and Environment on Friday. The patient is isolated, and health investigators are notifying their close contacts.

A spokeswoman for the county health department said the man is fully vaccinated, has mild symptoms and is recuperating at home. She said she has no booster information, and it remains unclear when he returned.

The state identified its first omicron case Thursday, in an Arapahoe County woman. She had also recently traveled to southern Africa. She has mild symptoms, officials said, and her close contacts have thus far tested negative.

The state is recommending any international travelers be tested within three to five days of returning, regardless of symptoms or known exposures. Rachel Herlihy, the state’s epidemiologist, said Thursday that the state was also working with the Centers for Disease Control and Prevention to develop increased travel monitoring.  

“Because the omicron variant is new, we are still gathering information about whether it is more contagious and whether it will cause people to have more severe disease,” Michelle Haas, the chief medical officer of Boulder County Public Health, said in a statement. She added that the identification of a new variant is “not unexpected.” “However, what little we do know would indicate there is still some protection from vaccines, and that masking and other mitigation strategies are still highly effective.”

The state health department uses targeted sequencing for specific samples, like the Boulder County case, as well as a random sampling of roughly 15% of positive cases statewide. It also uses wastewater testing to identify any variants moving on a community-wide level.

Gov. Jared Polis said Thursday that he wasn’t “terribly alarmed” by the variant’s arrival in Colorado, which was inevitable. He said the state’s detection systems indicate that “if community transmission is happening in Colorado, it’s very small.” Much remains unknown about the latest variant, and Polis said more information will likely come in the next two to three weeks.

Both the state and Boulder County said that current mitigation strategies – vaccines, boosters, masks, distancing and good hygiene – will remain the primary tools to ward off omicron, just as they were for delta and dominant strains before it.

The variant, first reported in South Africa last week, appears to have been spreading in Europe prior to its official identification. It’s been labeled a “variant of concern” because early signs suggest its more transmissible than the initial strain of the virus.

New COVID-19 cases in South Africa have burgeoned from about 200 a day in mid-November to more than 16,000 on Friday. Omicron was detected over a week ago in the country’s most populous province, Gauteng, and has since spread to all eight other provinces, Health Minister Joe Phaahla said.

Little is known about the new variant, but the spike in South Africa suggests it might be more contagious, said South Africa’s Sikhulile Moyo, the scientist who may have been the first to identify the new variant, though researchers in neighboring South Africa were close on his heels. Omicron has more than 50 mutations, and scientists have called it a big jump in the evolution of the virus.

It’s not clear if the variant causes more serious illness or can evade the protection of vaccines. Phaahla noted that only a small number of people who have been vaccinated have gotten sick, mostly with mild cases, while the vast majority of those who have been hospitalized were not vaccinated.

But in a worrisome development, South African scientists reported that omicron appears more likely than earlier variants to cause reinfections among people who have already had a bout with COVID-19. Herlihy, Colorado’s state epidemiologist, said earlier this week that the potential for reinfections from omicron are “certainly going to be a possibility.” 

The Associated Press contributed to this report.