The United States reported its first Omicron case identified in California and discovered in a traveller who returned from South Africa on 22 November and tested positive on 29 November.
That patient was fully vaccinated but did not have a booster shot, according to Dr. Anthony Fauci, the top US infectious disease official, who briefed reporters at the White House.
The person is in self-quarantine and all of the patient’s close contacts have tested negative, he said.
“We knew it was just a matter of time before the first case of Omicron would be detected in the United States,” Fauci said.
At least 23 other countries have reported Omicron infections, according to the World Health Organization, a week after it was declared a variant of concern by the UN health agency.
Omicron, designated is potentially more contagious than previous variants, although experts do not know yet if it will cause more or less severe COVID-19 compared with other strains.
The variant was first discovered by scientists in South Africa. The Biden administration moved late last month to restrict travel from southern Africa, where the variant was first identified and had been widespread.