A new strain of Omicron, called XE, is spreading in the U.K., and a few cases have been identified elsewhere in the world. Here’s what we do—and don’t—know about the variant.

What do we know about the XE variant so far?

XE is a hybrid of the two now-familiar strains of Omicron: BA.1 (the original Omicron strain) and BA.2 (the more infectious related strain that’s now dominant in the U.S. and other countries).