UK variant has become most dominant COVID strain in US, CDC says UK variant has become most dominant COVID strain in US, CDC says Replay Video UP NEXT The more contagious variant of coronavirus that was identified in the UK, the B-117 variant, has become the dominant strain in the U.S., CDC director Rochelle Walensky said on Wednesday. "Based on our most recent estimates from CDC surveillance, the B-117 variant is now the most common lineage circulating in the United States," Walensky told reporters at a White House briefing. Walensky’s comment was on schedule with previous predictions that the B-117 variant would become the more dominant strain by late March or early April.