The Centers for Disease Control and Prevention has released data Monday citing that the COVID-19 omicron variant now represents 73 percent of sequenced cases, and is considered as the dominant strain in the United States, CNBC reported.

It takes the place of the delta variant which now holds around 26.6 percent of sequenced cases for the week ending December 18, according to CDC. The fast-spreading Omicron grew from last week’s 12.6 percent, which was still way lower than 87 percent of the delta variant, based on the data.

In a week ending Dec. 11, the CDC said that the new COVID-19 omicron variant made up 2.9 percent of cases. The estimate for that week was however revised.

First found in late November in southern Africa, the omicron COVID-19 variant was considered by the World Health Organization as a “variant of concern” last Nov. 26.

While its arrival in the U.S. was not clear, the first case of omicron was recorded in California last Dec. 1. The infected person has manifested symptoms earlier on Nov. 15, as stated by CDC.

The extent of the seriousness of illness the variant can cause is still unknown, but it has already been proven to be highly infectious.

Omicron cases are even higher in some parts of the nation as compared to the 73 percent recorded in the U.S. In portions of the South, Southeast, Northeast, and Northwest, the CDC said it even reaches over 90 percent of cases.

The surge in omicron cases was recorded in New York City, its mayor Bill de Blasio said on Monday. The virus wave is expected to peak within weeks, he said.

The latest data posted on New York City’s health department website said average daily cases in the city increased by two-folds over the week ending Friday. More than 7, 200 cases per day are reported on a seven-day average – a 127 percent rise from the 3, 200 cases logged a week before.