COVID-19 variant XFG accounted for 0% of U.S. cases in May. By late-June, it became the third-most common strain.

WHO is monitoring the fast-spreading XFG "Stratus" COVID variant, now the third-most common US strain, as it spreads into Europe with no signs of greater severity.

Known officially as XFG, the variant was first detected in Southeast Asia back in January. For months, it flew under the radar in the States, barely any reported cases. However, Centers for Disease Control and Prevention (CDC) detailed XFG accounted for 14% of all U.S. cases by late June, making it the third most common variant in circulation.