According to the CDC, XBB was estimated to account for 18.3% of the COVID-19 cases in the United States in the week ended 24 December, up from 11.2% in the previous week.
As per details, XBB is a subvariant of the BA.5 variant which is targeted in the updated vaccines from Pfizer Inc/BioNTech SE and Moderna Inc, that the US government has authorized as booster shots.
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In November, US infectious diseases expert Anthony Fauci said the updated boosters - which target the original variant of the coronavirus as well as BA.4 and BA.5 subvariants - would still provide "some protection, but not the optimal protection" against the XBB variant.
BA.5 now represents just a small fraction of cases, having been overtaken by its offshoots, BQ.1 and BQ.1.1, which still remain the dominant variants but are on the decline.
The rise in cases of the new variant comes a week after the White House COVID response coordinator urged Americans to get their flu vaccines and updated COVID-19 boosters, pointing to rising cases in about 90% of the country ahead of the year-end holidays.
The XBB variant has been driving up cases in parts of Asia, including Singapore. While some experts have said it is more transmissible, it has not resulted in a surge in hospitalizations.
BQ.1.1 and BQ.1 are expected to account for 63.1% of cases in the United States, compared with 64.6% a week ago, the CDC said.
With Reuters inputs
