First confirmed US case of Omicron coronavirus variant detected in California

Tonight, CNN's Anderson Cooper and Chief Medical Correspondent Dr. Sanjay Gupta host a global town hall on the Omicron coronavirus variant and Dr. Anthony Fauci will answer viewer questions. Watch live at 9 p.m. ET on CNN.

(CNN)The United States' first confirmed case of the Omicron coronavirus variant has been identified in California.

In a White House news briefing, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the case was in an individual who traveled from South Africa on November 22 and tested positive for Covid-19 on November 29.

That individual, Fauci said, is self-quarantining and close contacts have tested negative for the coronavirus so far.

The person was fully vaccinated and is experiencing "mild symptoms, which are improving at this point," Fauci said.

Asked by CNN whether that person had a booster shot, Fauci said, "To my knowledge, no."

The California and San Francisco public health departments confirmed the case was caused by the Omicron variant through genomic sequencing conducted at the University of California at San Francisco, and the sequence was confirmed by the US Centers for Disease Control and Prevention.

Color Health said in a statement it returned the positive test result through an San Francisco Covid-19 testing program, and Omicron was identified in under 30 hours "from the time of collection to strain confirmation."