CDC director says Covid variant from UK is becoming the predominant strain in many parts of the U.S.

The highly contagious variant first identified in the U.K. is starting to become the predominant strain in many regions of the U.S., the head of the Centers for Disease Control and Prevention said Wednesday.

The variant, known as B.1.1.7, now accounts for 26% of Covid-19 cases circulating across the nation, CDC Director Dr. Rochelle Walensky told reporters during a White House news briefing on the pandemic. It is the predominant strain in at least five regions, she added.

The U.K. identified B.1.1.7, which appears to be more deadly and spread more easily than other strains, last fall. It has since spread to other parts of the globe, including the U.S., which has identified 11,569 cases across 51 jurisdictions as of Tuesday, according to the CDC.

Florida has the most confirmed cases of the new variant, according to a map of the CDC data, followed closely by Michigan, Wisconsin and California. Public health officials say they are working as quickly as possible to identify more cases.

Walensky said Wednesday she expects to see more infections in the U.S. due to the transmissibility of the B.1.1.7 variant. She urged the public to continue to practice pandemic safety measures, such as washing hands, wearing masks and practicing social distancing.

Walensky’s comments come two days after she issued a dire warning to reporters. She said Monday that she worried the nation is facing “impending doom” as variants spread and daily Covid-19 cases begin to rebound once again, threatening to send more people to the hospital.

“I’m going to pause here, I’m going to lose the script, and I’m going to reflect on the recurring feeling I have of impending doom,” Walensky said. “We have so much to look forward to, so much promise and potential of where we are and so much reason for hope, but right now I’m scared.”

An average of more than 63,000 daily new Covid-19 cases were reported in the United States over the last seven days, according to Johns Hopkins University data. That figure is up 16% from one week ago.

The White House’s chief medical advisor, Dr. Anthony Fauci, said Sunday the latest rise in cases is not being caused solely by new variants of the virus, adding that travel and easing of business restrictions are also a factor in the increase in infections.

“This is a critical moment in our fight against the pandemic,” Walensky said Wednesday. “We can’t afford to let our guard down.”

–CNBC’s Nate Rattner contributed to this report.