The Omicron subvariant "XBB" has made headlines as a so-called "nightmare" variant that has spread quickly in Asia and beyond (NBC Chicago, Yahoo News, CDC, STAT). The CDC estimates proportions of SARS-CoV-2 lineages circulating in the United States by week here: https://covid.cdc.gov/covid-data-tracker/#variant-proportions. For the week ending 22 October 2022, other Omicron variants represented a combined 100.0% percent share of COVID lineages in the US (see "%Total"). The question would close as of the week for which the threshold is reached—and weeks including "Nowcast" estimates (i.e., columns with "NOWCAST" at the top) would count—or else the week ending 8 April 2023. If the named sourced changes the way it presents the data, we will make the appropriate modifications to the resolution instructions.

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NOTE 11 November 2022: Any XBB sublineages would count. Whether an identified variant is considered to be XBB or a sublineage of XBB is dependent on the classification by the CDC.

NOTE 2 January 2023: The aggregate of XBB and its sublineages (e.g., XBB.1.5) would count.