The CDC started publicly tracking the prominence of four different forms of the delta variant on Aug. 9.
The delta variant causes more infections and spreads faster than early forms of COVID-19, the CDC reported. Vaccines continue to be highly effective at preventing hospitalization and death, including against this variant, according to the agency.
The CDC has tracked how prevalent delta, known as B.1.617.2, is in the U.S. as of July 31. The agency also started tracking AY.3, AY.2 and AY.1 strains of the variant, all known as "delta plus."
Below are the recent proportions of circulating delta variants:
B.1.617.2: 83.4 percent
AY.3: 9.1 percent
AY.2: 0.8 percent
AY.1: 0.1 percent