NEW YORK (AP) — Omicron has raced ahead of other variants and is now the dominant version of the coronavirus in the U.S.

Federal health officials said Monday that omicron accounted for an estimated 73% of new infections last week.

The Centers for Disease Control and Prevention numbers show nearly a six-fold increase in the proportion of infections in only one week.

Since the end of June, the delta variant has been the main version causing U.S. infections.

Scientists in Africa first sounded the alarm about omicron less than a month ago.

On Nov. 26, the World Health Organization categorized the new strain as a "variant of concern."

According to the Associated Press, the variant is now in about 90 countries.

It was first reported in the United States on Dec. 1.

The unidentified person, the CDC said was fully vaccinated, and tested positive after returning to the U.S. from South Africa on Nov. 22.

The variant has now shown up in several other states.

On Tuesday, President Joe Biden plans to address to issue "a stark warning of what the winter will look like for Americans that choose to remain unvaccinated," White House press secretary Jen Psaki tweeted.