The subvariant accounted for 49.5% of cases in the week ended Jan. 21, estimates from CDC showed.
XBB.1.5, which is currently the most transmissible variant, is an offshoot of XBB, first detected in October.
The now-dominant XBB-related subvariants are derived from the BA.2 version of Omicron.
An analysis from CDC showed on Wednesday that updated COVID-19 boosters from Pfizer Inc/BioNTech SE and Moderna helped prevent symptomatic infections against the new XBB-related subvariants.
(Reporting by Khushi Mandowara and Raghav Mahobe in Bengaluru; Editing by Krishna Chandra Eluri and Shailesh Kuber)