The XFG strain, nicknamed “Stratus,” is the predominant variant currently circulating. It has been on the rise since May in the United States and comprised 65% of variants in circulation as of Aug. 9, according to the CDC.

Here’s a closer look at the variants behind the surge and the places seeing the highest Covid rates. Like the other recent strains, Stratus is a subvariant of Omicron. Though it was first detected in Canada in January,