Scientists and health officials are keeping their eyes on a descendant of the omicron variant that has been found in at least 40 countries. It’s called BA.2. It is widely considered stealthier than the original version of omicron because particular genetic traits make it somewhat harder to detect. Some scientists worry it could also be more transmissible. But they say there’s a lot they still don’t know, including whether it evades vaccines better or causes more severe disease. To protect against it, doctors urge vaccination and the usual coronavirus precautions.