(CNN)The more contagious Delta variant of Covid-19 now makes up 83% of sequenced samples in the United States, US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Tuesday.
"This is a dramatic increase, up from 50% for the week of July 3," Walensky said in a Senate committee hearing.
Health experts have said the Delta variant is more transmissible than any other identified variant so far. "We should think about the Delta variant as the 2020 version of Covid-19 on steroids," Andy Slavitt, a former senior adviser to Joe Biden's Covid Response Team, told CNN last week.
"It's twice as infectious," Slavitt said. "Fortunately, unlike 2020, we actually have a tool that stops the Delta variant in its tracks: It's called vaccine."