The Orange County Health Care Agency reported 326 new daily infections on Dec. 21, up from a recent high of 143 seen last month.
Hospitalizations have also risen about 28% since the beginning of December.
On Dec. 17, the OCHCA reported the first confirmed case of the Omicron COVID-19 variant in Orange County.
The infected resident is a fully vaccinated adult male who had been traveling domestically outside of California, the agency said.
“The Omicron variant is highly transmissable and has already been identified in the United States and many countries around the world,” Deputy County Health Officer Dr. Matthew Zahn said in a statement.
“It’s important that we all do our part by following public health guidance to protect our loved ones and neighbors, especially those who are most vulnerable, during the holiday season.”