The B.1.1.7 variant, which was first identified in the U.K., is now the most dominant form of the coronavirus circulating in the U.S., according to comments made Wednesday by Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention. Research indicates that this strain of the virus is more infectious and more deadly. “The virus still has a hold on us,” she said during a White House briefing. “We need to remain vigilant.” The CDC said in January that it expected B.1.1.7 to be the most common form of the virus by the end of March. Walensky said that communities with high rates of community transmission should no longer allow youth sports that take place indoors or don’t allow six feet of spacing. She also said large events in those communities should be deferred.