A test tube labelled "COVID-19 Test Positive" is seen in front of displayed words "OMICRON SARS-COV-2" in this illustration taken December 11, 2021.

The omicron Covid-19 variant has quickly overtaken delta as the dominant strain of the virus across the U.S., accounting for 90% of the cases in some parts of the country, CDC director Dr. Rochelle Walensky said Wednesday.

The variant makes up more than 73% of the cases in the United States as of Saturday, according to the latest data released by the Center for Disease Control and Prevention. Last week, U.S. health officials said omicron accounted for 2.9% of all cases sequenced through Dec. 11, but later revised that number up to 12.6%.