First US confirmed omicron case in San Francisco

The U.S. recorded its first confirmed case of the omicron variant on Wednesday.

The infected person was identified as a traveler who had returned from South Africa on Nov. 22 and he developed mild symptoms and tested positive on Monday.

Researchers at the University of California, San Francisco obtained a sample from the patient on Tuesday evening and worked busily overnight to assemble the genetic sequence.

The person, who had had the two doses of the Moderna shot but had not been vaccinated long enough to receive a booster shot, is improving and agreed to remain in quarantine. All the individual's close contacts have been reached and have tested negative, officials said.