Omicron overtakes Delta, now accounts for 73% of all new U.S. COVID cases

The COVID-19 variant Omicron accounted for 73.2% of all new COVID-19 infections in the United States last week, according to data from the Centers for Disease Control and Prevention (CDC). 

In some regions of the United States such as New York, the Southeast, the Pacific Northwest and the industrial Midwest, Omicron accounts for 90% or more of all new infections.

More than 650,000 Omicron infections may have occurred in the United States last week, according to the Associated Press. 

In less than a month, Omicron overtook Delta as the primary COVID-19 variant in the U.S.

The World Health Organization first identified Omicron as a variant in November, when more than 99.5% of U.S. cases were Delta, according to the CDC.

CDC Director Rochelle Walensky still encouraged the public to get "vaccinated & boosted if you are eligible AND implement layered prevention measures-wear a mask indoors & consider taking an at home #COVID19 test prior to gathering with others."

"I anticipate that over time that delta will be crowded out by omicron," Walensky said.

The South African doctor who helped discover the new variant reported that the symptoms she had seen were "extremely mild" at that point in late November. 

New York City Mayor Bill de Blasio on Monday said the Omicron cases "are more mild than what we've experienced previously" in the Big Apple.

Some experts warn that the optimism may be premature. 

An Imperial College London study revealed Friday that the risk of reinfection from Omicron is more than five times higher than Delta and has no sign of being milder, according to Reuters.

The U.K. study is at odds with data coming out of South Africa, where the vaccine efficacy is proving much higher against Omicron.

CDC officials do not have estimates of how many people have been hospitalized or died due to Omicron.