US reports 1st case of Omicron

The US recorded its first confirmed case of the omicron variant Wednesday - in a vaccinated traveller who returned to California after a trip to South Africa - as scientists around the world race to establish whether the new, mutant version of the coronavirus is more dangerous than previous ones.

Dr Anthony Fauci, the United States' top infectious-disease expert, announced the finding at the White House.

"We knew it was just a matter of time before the first case of omicron would be detected in the US," he said.

The infected person was identified as a traveller who had returned from South Africa on Nov. 22, developed mild symptoms and tested positive for Covid-19 Monday. Researchers at the University of California, San Francisco obtained a sample from the patient Tuesday evening and worked feverishly overnight to assemble the genetic sequence.