The first known case of the omicron coronavirus variant has been detected in the U.S. just days after its rapid spread in South Africa and numerous mutations prompted worldwide concern. The California and San Francisco Departments of Public Health have confirmed that a recent case of COVID-19 among an individual in the state was caused by omicron. The person was a traveler who returned from South Africa on Nov. 22 and was fully vaccinated. The person had mild symptoms that are improving. Experts had been warning that the variant was likely already in the U.S. in the days before the announcement. "When you have a virus that is showing this degree of transmissibility and you're having travel-related cases they've noted in other places already, when you have a virus like this, it almost invariably is going to go all over," said presidential medical adviser Dr. Anthony Fauci in a Saturday NBC interview. Fauci applauded the Biden administration's move to restrict travel from eight African countries, including South Africa, in an effort to slow the variant's spread to the United States. The Centers for Disease Control and Prevention and the U.S. Department of State raised their alert levels for the region, each recommending against travel.