XBB.1.16 ‘Arcturus’ Is New Covid-19 Variant Under Monitoring By The WHO In the U.S,, the XBB.1.16 accounted for an estimated 7.2% of all Covid-19 samples from April 9 to April 15, according to the Centers for Disease Control and Prevention (CDC). That’s up from 3.9% the week before and 2.1% the week prior to that.