Omicron Variant Detected in More Areas of Yolo County

Healthy Davis Together and Genome Center Find 42 Cases of Virus

COVID test tubes in dark
COVID-19 tests are prepared at the UC Davis Genome Center. (Gregory Urquiaga/UC Davis)

Healthy Davis Together issued the following news release today (Dec. 22):

The UC Davis Genome Center has detected and confirmed an additional 42 cases of the B.1.1.529 (omicron) variant of SARS-CoV-2, the virus that causes COVID-19, in Yolo County, specifically in Davis, El Macero, West Sacramento and Woodland.


Testing locations and hours in Davis, Woodland and throughout Yolo County are available on the Healthy Davis Together website. Appointments are preferred, but walk-ins are accepted at most testing locations. Parking is free.

The Genome Center had previously detected only two omicron cases, both in West Sacramento. The variant has also been detected in trace amounts in the city of Davis’ sewage through Healthy Davis Together’s wastewater monitoring initiative.

Omicron has been identified as a variant of concern by the U.S. Centers for Disease Control and Prevention, or CDC, and the World Health Organization, or WHO. The CDC is working with other U.S. and global public health and industry partners to learn more about the variant, including how severe its cases are compared to other variants and the amount of protection provided by existing vaccines.

The Genome Center screens every positive COVID-19 test conducted by Healthy Davis Together for all currently known SARS-CoV-2 variants of concern so that action can be taken to alert and protect the community. Tests administered from Dec. 12 to 18 yielded the 42 new cases.

Several of the Davis cases have been linked to a single workplace holiday party. The party, with approximately 50 attendees, and subsequent workplace spread are associated with an outbreak of at least 16 cases, of which 10 are known so far to be omicron. Of the 16 people infected, all were fully vaccinated and eight had received their booster shots. At this time, all known omicron cases are in isolation or have completed isolation.

‘Take additional precautions’

“The omicron variant is spreading quickly in Yolo County and accounted for 41% of new cases detected by the UC Davis Genome Center last week,” said Aimee Sisson, Yolo County public health officer.

“The spread of omicron is coming at a time when many people are traveling and gathering for the holidays,” she said. “Everyone, including fully vaccinated persons, should take additional precautions right now. Wear a mask that fits and filters well when you are indoors, improve indoor ventilation with portable air filters and ask everyone attending a gathering to test right before the event. In addition, anyone who isn’t vaccinated or boosted should get vaccinated as soon as possible in order to protect themselves against severe COVID-19 illness.”

Wastewater monitoring

The detection of the omicron variant through clinical testing comes as genetic markers of the variant have been identified in the city’s wastewater by Healthy Davis Together and its partner, the Sewer Coronavirus Alert Network, or SCAN. The Davis sewage treatment plant is one of eight that SCAN monitors by testing daily samples of solids in wastewater, which carry signs of the virus and its variants if present in a community. Wastewater monitoring is another tool that can be used as an early detection system for new strains and future spikes of COVID-19.

“The information collected through Davis’ wastewater monitoring program can be useful in our long-term community effort to reduce the spread of COVID-19,” said Brad Pollock, director of Healthy Davis Together and chair of the UC Davis Department of Public Health Sciences.  

How to stay safe

Here are the most important things people can do right now to prevent the spread of COVID-19, including the omicron variant:

  • Get vaccinated. With the recent approval of the Pfizer vaccine for children 5-11 years of age, HDT strongly encourages everyone 5 years and older to get vaccinated.
  • If you’re already vaccinated, get boosted two months after a Johnson & Johnson vaccine or six months after the second Moderna or Pfizer vaccine.
  • Get tested if you have symptoms or have been exposed to someone infected with COVID-19.
  • If you are planning to travel or gather, it’s recommended that you get tested one to three days prior to and three to five days after traveling or gathering, even if you’re vaccinated.
  • If you aren’t vaccinated yet, it’s important to get tested regularly.
  • Follow local mask guidance. N95s, KN95s and KF94s provide additional protection and are good options for people more vulnerable to severe disease, for example, older adults and people with underlying conditions.
Healthy Davis Together is a joint project of UC Davis and the city of Davis to prevent the spread of COVID-19 in our community and facilitate a coordinated and gradual return to regular city activities and student life. Comments and questions are welcome by email.

Media Resources

Media contact:

  • Karen Nikos-Rose, UC Davis,, 530-219-5472

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