The more transmissible Delta variant now accounts for 83% of COVID-19 cases in the United States, Centers for Disease Control and Prevention director Rochelle Walensky said during a Senate hearing Tuesday.

Why it matters: The "dramatic increase," up from 50% on July 3, has led to a rise in virus-related deaths, Walensky told lawmakers.

• COVID fatalities have risen by nearly 48% since last week to an average of about 239 per day, according to Walensky.

What they're saying: The CDC director also said that the percentage of cases from the Delta variant is "even higher" in some parts of the country, "particularly in areas of low vaccination rates."

• "To date, our data indicates that vaccines are available to neutralize the circulating variants in the United States and provide protection against severe disease, hospitalization, and death," Walensky added.
• "The message from CDC remains clear: the best way to prevent the spread of COVID-19 variants is to prevent the spread of disease and vaccination is the most powerful tool we have."
• "Each death is tragic and even more heartbreaking when we know that the majority of these deaths could be prevented with a simple, safe, available vaccine."