Experts say BA.5 is cause for worry: “The worst version of the virus that we’ve seen,” said Dr. Eric Topol, the founder of Scripps Research Translational Institute. Along with another Omicron subvariant, BA.4, the two strains now account for the majority of new U.S. COVID cases, according to the latest data from the Centers for Disease Control and Prevention — but BA.5 (36.6%) is spreading a lot faster than BA.4 (15.7%). In just a few weeks, BA.5 ;will be the dominant strain in the U.S.