US health officials on Wednesday confirmed the first case of a new strain of the coronavirus “Omicron” in a man returning from South Africa. The case was detected in California.

According to the Centers for Disease Control and Prevention (CDC), the person, who was fully vaccinated, had returned from a trip to South Africa on November 22 and tested positive on November 29. “The person is in self-quarantine and all close contacts have been contacted and tested negative so far,” White House chief medical adviser Dr Anthony Fauci said in a press briefing. Genomic sequencing was performed at the University of California, San Francisco, according to the CDC, confirming that it is indeed the highly infectious Omicron variant.

The World Health Organization (WHO) warned on Wednesday that since South Africa first reported it to the World Health Organization, it has been confirmed in 23 countries and their numbers are expected to rise. While the discovery of Omicron has sparked panic around the world, the WHO says this new strain has yet to reveal all its secrets.