WASHINGTON, United States -- Senior government scientist Anthony Fauci said Monday 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," Fauci said on ABC's "Good Morning America."

Fauci also encouraged people to get coronavirus vaccines or boosters quickly, rather than waiting 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," Fauci said.

"I would strongly suggest you get boosted now."

The World Health Organization 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 first detected, 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 vaccines, tests and treatments.

The United States has restricted travel from eight southern African countries, and northern neighbor 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 traveled to Nigeria.

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