Is XBB.1.5 common?

Worldwide, XBB.15 is still fairly rare. As of early January, it accounted for less than 1 percent of coronaviruses being sequenced. For now, it is most common in certain hot spots, like the northeastern United States, where it makes up about three-quarters of new cases.

Is XBB.1.5 a cause for serious concern?

Yes. Even though it is still rare, it is multiplying much faster than other subvariants of Omicron. However, many experts doubt it will produce a record-breaking wave of infections the way Omicron did in early 2021.