WEST SACRAMENTO (CBS13) — Yolo County on Thursday confirmed there were multiple confirmed cases of the COVID-19 Omicron variant at River City High School in West Sacramento.

John Fout, the public information officer for the county, said there were two confirmed cases and three presumed cases among five students.

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Four of the students were all in the same classroom, according to Fout, and the fifth student was a family member of one of the other four students. Additionally, another family member of one of the students is also part of the outbreak, the county said.

All six of the cases have had either mild or no symptoms.

Due to there being more than three cases from one classroom, county Public Health Officer Dr. Aimee Sisson declared the situation an outbreak, Fout said.

“The detection of an Omicron outbreak at a Yolo County school is not surprising because we already knew that Omicron was present in Yolo County, and schools are a part of the Yolo County community. This outbreak illustrates that the Omicron variant is circulating in our community and is not just a risk for those who have traveled. Omicron is here, and Omicron can spread quickly,” Dr. Sisson in a news release.

Two of the five students were fully vaccinated, but without booster shots, and had not traveled recently.

“This is consistent with data coming from the rest of the world that vaccines are less effective at preventing Omicron infection,” Fout said in a statement to CBS13.

More testing is being done on the River City campus Thursday and Friday, and students and staff will be sent home with testing kits to use before they return to campus from winter break in January.

“I want to hang out with friends, but I also want to be careful,” said student Zhonee Reed.

Reed’s basketball bubble at River City High School plays and practices together.

“You always have to have a selective group,” Reed said.

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But how does Yolo County Health and Human Services know for sure the cases are the Omicron variant?

“We were contacted by the genome center at UC Davis, letting us know their genotyping had identified two cases of the Omicron variant,” Dr. Sisson said.

The county tracked the cases to students at River City.

“The genome center has a history of success. So we’re confident in the Omicron label,” Dr. Sisson said.

The biggest concern moving forward is that school is out for Christmas.

“As we head into the holidays knowing we could have students bringing the virus with them to holiday gatherings,” Dr. Sisson said.

The county is asking students and staff to test for COVID-19 before and after the holidays.

“We’re all tired, I’m tired of Omicron. We’re all tired of COVID but I think now is not the time to let down our guard,” Dr. Sisson said.

Says Dr. Sisson.

Unvaccinated students affected by the outbreak have been told to quarantine.

CBS13 did reach out to the Washington Unified School District directly to ask about their protocol moving forward and if they’re considering a return to fully online classes.

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We did not immediately hear back.