Dec. 1, 2021 -- The first case of the Omicron variant of the coronavirus in the United States was confirmed by officials today in an individual in California who had recently traveled to South Africa. He or she was fully vaccinated against COVID-19 and experienced only "mild symptoms that are improving," officials with the CDC said.

The patient, who was not named in the CDC's annoucement of the first U.S. case of the Omicron variant on Wednesday, is self-quarantining.

"All close contacts have been contacted and have tested negative," officials said. 

White House COVID-19 Response Coordinator Jeff Zients reiterated that the first case was not unexpected. 

"The president’s medical team continues to believe that existing vaccines will provide some level of protection against severe illness from Omicron, and individuals who have gotten boosters have even stronger protection," Zients said in a statement. 

"This new variant is cause for continued vigilance, not panic," he said. "We know what it takes to limit the spread of COVID: Get vaccinated, get boosted, and take public health measures like masking and distancing."

The Omicron variant, first identified in South Africa, has been reported in countries around the world in recent days. Hong Kong, the United Kingdom, and Germany each reported this variant, as have Italy and the Netherlands. Over the weekend, the first North American cases were identified in Canada. It's currently been found in at least 23 countries, the World Health Organization said Wednesday. 

Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, announced over the weekend that this newest variant was likely already in the U.S., telling ABC’s This Week its appearance here was “inevitable.”

Similar to previous variants, this new strain likely started circulating in the U.S. before scientists could do genetic tests to confirm its presence.

The WHO named Omicron a “variant of concern” on Friday, even though much remains unknown about how well it spreads, how severe it can be, and how it may resist vaccines. In the meantime, the U.S. enacted travel bans from multiple South African countries.

It remains to be seen if Omicron will follow the pattern of the Delta variant, which was first identified in the U.S. in May and became the dominant strain by July. It’s also possible it will follow the path taken by the Mu variant. Mu emerged in March and April to much concern, only to fizzle out by September because it was unable to compete with the Delta variant.