The highly infectious Delta variant is now the dominant coronavirus strain in the U.S., according to the latest Centers for Disease Control and Prevention estimates, accounting for more than half of the country’s Covid-19 infections over the last two weeks and risking new waves of infection as the country fully reopens despite dangerously low levels of vaccine uptake in some areas and groups, including children.
The Delta variant, which was first detected in India and is also known as B.1.617.2, now accounts for 51.7% of Covid-19 cases in the U.S., according to the latest CDC estimates from the two week period between Jun. 20 and Jul. 3.
The Alpha or B.1.1.7 variant, which was first identified in the U.K. and became the dominant U.S. strain in April, now makes up 28.7% of cases.
The Delta variant has spread rapidly to become the dominant U.S. variant: It represented just 10% of cases around a month ago and around 30% of cases between Jun. 6 and Jun 19.
In two of 10 regions the CDC monitors—one covering Iowa, Kansas, Missouri, and Nebraska, and the other Colorado, Montana, North Dakota, South Dakota, Utah and Wyoming—the Delta variant already accounts for 80.7% and 74.3% of cases respectively.
Though Delta has driven a wave of new infections among unvaccinated groups in highly vaccinated countries—notably in children and young people—the CDC has so far declined to follow the World Health Organization in encouraging vaccinated Americans to wear masks and the White House has said it will leave decisions on new pandemic restrictions to individual states.