Public health official and President Joe Biden’s chief medical adviser Dr. Anthony Fauci confirmed on Wednesday that the first case of the Omicron variant of COVID-19 has been identified in the United States.

Speaking during a White House press briefing, Fauci said the case was found in California, adding that the patient traveled from South Africa to San Francisco on Nov. 22 and tested positive for COVID-19 on Monday. Fauci said: “The individual is self-quarantining and all close contacts have been contacted and all close contacts, thus far, have tested negative. The individual was fully vaccinated and experienced mild symptoms, which are improving at this point. So this is the first confirmed case of COVID-19 caused by the Omicron variant detected in the United States.”

The World Health Organization designated the Omicron variant a “variant of concern” last Friday after it was first identified in South Africa. The organization said Omicron has a large number of mutations and may spread at faster rates than other variants. News of the variant’s spread prompted countries across the globe to shut down travel from certain areas of Africa, though it has been detected in European countries.

Biden on Monday sought to calm fears about the new variant, saying that current vaccines should be adequate to combat Omicron, and added that it was a “cause for concern, not a cause for panic.” Vaccine makers said that they are testing their COVID-19 vaccines against the new variant, saying it may require new boosters that can target the strain.