Live updates: follow the latest news on Covid-19 variant Omicron
The first confirmed case of the new Omicron variant of coronavirus has been detected in the western state of California, the US Centres for Disease Control and Prevention (CDC) said on Wednesday.
Omicron has been labelled a “variant of concern” by the World Health Organisation and was reported in more than 20 countries before the first infection in the US was discovered by health authorities in San Francisco.
“The individual was a traveller who returned from South Africa on November 22, 2021,” the health agency reported in a statement.
“The individual, who was fully vaccinated and had mild symptoms that are improving, is self-quarantining and has been since testing positive. All close contacts have been contacted and have tested negative.”
The person was vaccinated but did not have a booster dose, President Joe Biden's medical adviser, Dr Anthony Fauci, said in the White House press briefing on Wednesday.
The US restricted travel from countries in southern Africa, where Botswana and South Africa were the first to discover the variant.
Mr Biden is expected to speak on any additional international travel measures on Thursday. The Washington Post and Bloomberg say the Biden administration and CDC are considering stricter testing requirements.
Much remains unknown about the new variant, including whether it is more contagious than previous strains, whether it makes people more seriously ill or whether it can overcome the vaccine.
The president has tried to quell alarm over the variant, saying it was a “cause for concern, not a cause for panic".
California Governor Gavin Newsom tweeted on the news: “CA’s large-scale testing and early detection systems have found the Omicron Covid-19 variant in California. We should assume that it’s in other states as well.”
Dr Fauci said more would be known about the strain in two to four weeks as scientists grow and test lab samples of the virus.
“What's happening now is another example of why it's important for people to get vaccinated,” he said from the White House, also advising fully vaccinated people to take their booster doses.
A reporter asked the doctor about when the Covid-19 health crisis will end.
“This will end. I promise you that. This will end,” Dr Fauci responded.
Associated Press contributed to this report