WASHINGTON (AFP) - Senior government scientist Anthony Fauci said on Monday (Nov 29) that the United States was on high alert for the new Covid-19 variant and urged people to get vaccinated after Canada confirmed its first cases of the new strain.

"No confirmed cases (of Omicron), but obviously we're on high alert," Dr Fauci said on ABC's Good Morning America.

He also encouraged people to get coronavirus vaccines or boosters quickly, rather than wait for pharmaceutical companies to tailor doses specifically to the Omicron variant.

"A variant like this, although there's a lot we don't know about it, one thing we do know is that vaccinated people do much, much better than unvaccinated people, and particularly when you boost someone," he said.

"When you get vaccinated and boosted and your level (of antibodies) goes way up, you're going to have some degree of protection, at least against severe disease," he added.

"I would strongly suggest you get boosted now."

The World Health Organisation (WHO) has listed Omicron as a "variant of concern", and countries around the world are now restricting travel from southern Africa, where the new strain was identified, and taking other new precautions.

The WHO says it could take several weeks to know if there are significant changes in transmissibility, severity or implications for Covid-19 vaccines, tests and treatments.

The United States has restricted travel from eight southern African countries, and northern neighbour Canada has restricted travel from seven.

On Sunday, Canada said it had detected its first cases of the new strain - in two people who had recently travelled to Nigeria.

Both patients are in isolation while public health authorities trace their possible contacts, said officials.