The number of COVID-19 cases in the United States rose 10% this week as the highly contagious delta variant gained further ground, the CDC said Thursday. The country's lagging vaccination rate coupled with the "hypertransmissible delta variant" could account for the increase, CDC Director Dr. Rochelle Walensky said during a White House briefing. The variant, which was first detected in India, now accounts for a quarter of all new cases, and has been detected in all 50 states.