The highly transmissible omicron variant accounted for an estimated 95% of all new COVID-19 infections last week, the U.S. Centers for Disease Control and Prevention said Tuesday.

That number is up from 77% the previous week. The delta variant now accounts for less than 5% of cases.

About a month ago, omicron was responsible for less than 1% of U.S. infections, according to CDC data. 

The CDC estimates are based on genomic-sequencing data, and while the weekly numbers have been significantly revised at times, they still paint a picture of omicron, which was first identified in South Africa, taking over as the United States' overwhelmingly dominant strain in a short time.

While the omicron mutation makes it easier for the virus to spread and evade vaccines and some treatments, the variant is less likely to cause severe illness, studies say.

On Monday, according to data from Johns Hopkins University, the U.S. reported a record-high 1.08 million COVID-19 cases, although that includes a backlog of cases reported after a number of states paused over New Year’s Day weekend.

Still, the seven-day average of 480,283 cases is nearly twice as high as it was at last winter’s peak. Hospitalizations, meanwhile, are up 32% from a week ago, the U.S. Department of Health and Human Services said Monday. The seven-day average for COVID-19 deaths has remained relatively steady in recent weeks, currently at 1,236, according to Johns Hopkins.

Last week, the CDC reported omicron accounted for 58.6% of new infections but revised that number to 77% Tuesday.