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YOLO COUNTY, Calif. (KTXL) — Yolo County reported Thursday that it has identified its first case of the omicron variant.

According to Yolo County officials, Healthy Davis Together and the UC Davis Genome Center detected the case in a West Sacramento resident who recently traveled domestically. That person is vaccinated.

That person is in isolation and contact tracing has started.

“The detection of the potentially highly transmissible Omicron variant is concerning, especially with more people traveling and visiting with friends and family for the holidays,” said Yolo County Public Health Officer Dr. Aimee Sisson. “There is still a lot we don’t know about the Omicron variant, but this detection is a reminder that we must remain vigilant in using the tools we have to protect ourselves against Delta and Omicron, including vaccination, boosters, testing and following local guidance on mask wearing.”

The United State’s first identified case of the omicron variant was detected in San Francisco at the start of the month. A vaccinated traveler who tested positive for the variant had returned to California after a trip to South Africa.

Since then, the variant has been detected in cities across the state.

Days after the case out of San Francisco, five confirmed cases of the variant were reported out of Alameda County. Those five people were part of a larger group of a dozen vaccinated individuals who tested positive for COVID-19. They were all linked to a Nov. 27 wedding in Wisconsin, “which one of these individuals attended upon return from international travel,” the Alameda County Department of Public Health said.

Gov. Gavin Newsom said the discovery of the omicron variant “was predictable.” The governor and the state’s top health officials said California’s access to biotech and genomic sequencing efforts made it inevitable the first case would be detected in the state.

With the omicron variant now in California, Newsom said there are no plans to shut down schools and businesses. Pfizer has now said that a booster dose of its COVID-19 vaccine may protect against the new variant, even though the initial two doses appear significantly less effective.