CDC wastewater also shows the XFG variant — nicknamed stratus — is most common in the U.S. Stratus can cause a “razor blade” sore throat and is considered a “variant under monitoring” by the World Health Organization. The WHO said the variant is only marginally better at evading people's immune systems and vaccines still work against it.

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,