U.S. President Joe Biden on Monday said at the White House that Omicron will appear in the U.S. "sooner or later."

"Sooner or later, we're going to see cases of this new variant here in the United States. We'll have to face this new threat just as we face those who have come before it," he said.

Biden said the new Omicron coronavirus variant is "a cause for concern, not a cause for panic," and he told reporters that lockdown was not an option for the time being. 

The Omicron variant could slow the recovery of the U.S. economy and labor market and heighten uncertainty regarding inflation, Federal Reserve Chair Jerome Powell wrote in prepared testimony he is set to deliver to the Senate Committee on Banking, Housing and Urban Affairs on Tuesday.

The U.S. Centers for Disease Control and Prevention also strengthened recommendations for booster doses, noting that all adults should get a booster shot six months after the second dose.