Fauci warns of bleak winter with Omicron 'raging through the world'

Top US pandemic advisor Anthony Fauci on Sunday warned of a bleak winter ahead as the Omicron coronavirus variant spurs a new wave of infections globally, sparking restrictions and concerns over hospital capacity. 

"One thing that's very clear... is (Omicron's) extraordinary capability of spreading," Fauci said.

"It is just... raging through the world."

Since it was first reported in South Africa in November, Omicron has been identified in dozens of countries, prompting many to reimpose travel restrictions and other measures.

Despite indications it is not more severe than the Delta variant -- currently still the dominant strain -- the heavily mutated Omicron has been shown in early data to have a worrying resistance to vaccines and higher transmissibility.

Fauci also cautioned against too much optimism over Omicron's severity, noting that in South Africa, while the hospitalization-to-case ratio is lower than with Delta, this could be due to underlying immunity from widespread previous infections.

"No matter how you look at it," he said, "when you have so many, many infections, even if it is less severe, that overcomes this slight to moderate diminution in severity."

"Our hospitals, if things look like they're looking now in the next week or two, are going to be very stressed," particularly in areas of the country with low levels of vaccination, Fauci said.

On Sunday, US Senators Elizabeth Warren and Cory Booker each said separately on Twitter that they had tested positive for Covid-19 despite being vaccinated and boosted, and were experiencing mild symptoms.

Neither indicated whether they had been infected with Omicron.

Fauci urged unvaccinated Americans to get a shot and the vaccinated to get boosters, which have been shown to re-up protection.