Fauci says early data on the Omicron variant is 'encouraging,' but we don't yet truly know how deadly it is

• Anthony Fauci said on Sunday that South Africa's initial data on Omicron was "a bit encouraging."
• But he added that it was too early to determine whether the new variant was less deadly than Delta.

Early data from South Africa on the new Omicron coronavirus variant was "encouraging," Dr. Anthony Fauci said.

But it was too early to tell whether Omicron caused only mild infection, Fauci, President Joe Biden's chief medical advisor, told CNN's "State of the Union" on Sunday.

Fauci said that so far there didn't seem to be a "great degree of severity" to the Omicron variant, which has a high number of mutations in the part of the virus that attaches to human cells.

"But we really got to be careful before we make any determinations whether it's less severe" than Delta, Fauci said. The highly infectious Delta variant, which itself has mutations that help it avoid the immune response, is the most common variant in the US.

"Thus far, the signals are a bit encouraging" regarding Omicron's severity, Fauci said. He added that Omicron was "clearly" becoming the most common variant in South Africa — the country that sounded the alarm less than two weeks ago, and where Omicron is fast spreading.

The average number of new daily COVID-19 cases per million in South Africa increased more than 17-fold from November 22 to 167 on Sunday, Oxford University's Our World in Data showed.

As of Saturday there were 3,255 South Africans admitted to the hospital with COVID-19, official figures indicated. There were 16,366 new COVID-19 cases that day, the data showed.

Experts worldwide are still racing to determine whether Omicron's unusual mutations make the virus more deadly or infectious than Delta, and whether it can evade vaccines.

Dr. Maria Van Kerkhove, the COVID-19 technical lead at the World Health Organization and a US infectious-disease doctor, told "Face the Nation" on Sunday that initial reports suggested the Omicron variant caused a milder disease than Delta, but it was too early to say because it can take weeks for people to go through the full course of their infection.

Kerkhove cautioned that even if the disease caused by Omicron was mild, it was important to "act fast now" and take measures to control its spread. "More cases can mean more hospitalizations. More hospitalization can mean more death. We don't want to see that happening on top of an already different situation with Delta circulating globally," she said.

Fauci said that 99.9% of new COVID-19 cases in the US were caused by Delta. Fifteen US states have detected Omicron, he added.

Boosters are going to be "really critical" in whether the US can handle both variants, Fauci said. About 23% of fully vaccinated Americans have had a booster shot, the Centers for Disease Control and Prevention said.