By Kanishka Singh

(Reuters) -Top U.S. infectious disease expert Anthony Fauci said there was still a danger of a surge in hospitalization due to a large number of coronavirus cases even as early data suggests the Omicron COVID-19 variant is less severe.

"The only difficulty is that if you have so many cases, even if the rate of hospitalization is lower with Omicron than it is with Delta, there is still the danger that you will have a surging of hospitalizations that might stress the healthcare system," Fauci said in an interview on Sunday with CNN.

The Omicron variant was estimated to be 58.6 percent of the coronavirus variants circulating in the United States as of December 25, according to data from the U.S. Centers for Disease Control and Prevention (CDC).

The sudden arrival of Omicron has brought record-setting case counts to countries around the world and dampened New Year festivities around the world..

"There will certainly be a lot more cases because this is a much more transmissible virus than Delta is," Fauci said on CNN.

However, "It looks, in fact, that it [Omicron] might be less severe, at least from data that we've gathered from South Africa, from the UK and even some from preliminary data from here in the United States," Fauci said.

Fauci added that the CDC will soon be coming out with a clarification on whether people with COVID-19 should test negative to leave isolation, after confusion last week over guidance that would let people leave after five days without symptoms.

The CDC had reduced the recommended isolation period for people with asymptomatic COVID to five days, down from 10. The policy does not require testing to confirm that a person is no longer infectious before they go back to work or socialize, causing some experts to raise questions.

"You're right. There has been some concern about why we don't ask people at that five-day period to get tested. That is something that is now under consideration", Fauci told ABC News in a separate interview on Sunday. "I think we're going to be hearing more about that in the next day or so from the CDC."

U.S. authorities registered at least 346,869 new coronavirus on Saturday, according to a Reuters tally. The U.S. death toll from COVID-19 rose by at least 377 to 828,562.

(Reporting by Kanishka Singh in Bengaluru; Editing by Daniel Wallis and Mark Porter)