According to CDC Director, Dr. Rochelle Walensky, the number of cases is expected to keep climbing.
"We know we have several dozen cases and we’re following them closely and everyday hearing about more probable cases," she said.
The CDC director spoke to ABC News Sunday morning about the new variant – already found in dozens of countries. However, she said the man concern right now is the delta variant, which accounts for thousands of new cases.
"You know the first thing I think we should say is we have about 90-100,000 cases a day, in 99.9% of them is the delta variant," she said.
The omicron variant, first detected in South Africa, has several mutations potentially leading to increased antibody resistance and transmissibility.
"What we don’t quite know is how transmissible it will be, will our vaccines work, will it lead to more severe diseases," she said.
Saturday, Wisconsin reported its confirmed case of the COVID-19 omicron variant. Officials say a Milwaukee County man, who was fully vaccinated and received a booster shot, had mild symptoms after a recent trip to South Africa.
Dr. Anthony Fauci told CNN's “State of the Union” Sunday that it’s still too early to determine the severity of the new variant.
"Thus far, it does not look like there's a great degree of severity to it," Fauci said. "But we have really got to be careful before we make any determinations that it is less severe or it really doesn't cause any severe illness, comparable to delta."
Health officials say although there are still a lot of unknowns about the new variant, mitigation efforts and vaccinations remain effective.
"The more mutations a single variant has, the more immunity you need to have to combat that variant, that’s why we’re really pushing to get more people vaccinated and more people boosted," said Dr. Walensky.
As of Monday, international travelers must provide proof of a negative COVID-19 test within one day of departure for the U.S.
Previously a test could be taken up to three days before entering the country.