Scientists and health officials around the world are keeping their eyes on a descendant of the Omicron variant that has been found in more than 50 countries, including the United States. This version of the Coronavirus, which scientists call BA.2, is widely considered stealthier than the original Omicron because particular genetic traits make it somewhat harder to detect.

Danish scientists reported this week that preliminary information suggests it may be one-and-a-half times more contagious than the original variant. But scientists say there’s a lot they still don’t know about it, including whether it causes more severe disease.