Delta variants: CDC director says highly infectious strains account for 83% of new COVID-19 cases in the United States The director of the US Centers for Disease Control and Prevention said on Tuesday that the number of new COVID-19 cases caused by the highly contagious Delta variant has increased sharply since early July. Dr. Rochelle Walensky told the U.S. Senate Committee This variant now accounts for 83% of new cases in the United States, according to CNNThis is an increase from 50% in the week of July 3. According to a CNN report, Andy Slavitt, a former senior adviser to President Joe Biden’s COVID response team, said: “It’s twice as infectious.” “Fortunately, with The difference in 2020 is that we actually have a tool to stop the development of the Delta variant: it is called a vaccine.”