UK variant now most common COVID strain in U.S. -CDC

"Based on our most recent estimates from CDC surveillance, the B.1.1.7 variant is now the most common lineage circulating in the United States," Walensky said.

She also said at the briefing that the United States has delivered about 3 million COVID-19 vaccine doses per day on average over the past week, up 8% over the previous 7-day average.

Still, daily U.S. cases of novel coronavirus are averaging 63,000 over the past seven days, up 2.3% from the previous 7-day average, she told reporters at a White House briefing.