It's an extra-contagious version of the omicron variant, but it doesn’t seem to cause more severe disease.
Since it was first identified in November, BA.2 has been spreading around the globe, driving new surges in parts of Asia and Europe. It's now the dominant coronavirus version in the U.S. and more than five dozen other countries.
It was given the “stealth” nickname because it looks like the earlier delta variant on certain PCR tests, says Kristen Coleman at the University of Maryland School of Public Health. The original omicron, by contrast, is easy to differentiate from delta because of a genetic quirk.
