Why XBB.1.5 will not get a Greek letter: WHO

The XBB.1.5 omicron subvariant does not warrant its own Greek letter name — at least not yet — because data suggests it is behaving similarly to other omicron sublineages in terms of transmissibility, severity, immune escape and its effect on interventions, according to the World Health Organization. 

"When that changes, we will be using these Greek letters. We're not afraid to use these Greek letters or to assign different subvariants, but we have a criteria by which we do this through our technical advisory group for virus evolution," Maria Van Kerkhove, PhD, the WHO's technical lead on COVID-19, said during a Jan. 11 media briefing.

Health officials are still learning about XBB.1.5, with current assessments based on limited sequencing data that is mostly from the U.S., where the strain is estimated to account for at least 28 percent of cases. 

"It's an incredibly transmissible variant like all [omicron sublineages] are," Dr. Vankerhove said. "We don't yet have data on severity, and that is under assessment in the United States but also elsewhere … there's no indication of an increase of severity or decrease of severity compared to other omicron subvariants," she said. 

Scientists have been at odds over whether nicknames such as "Kraken," now being used to refer to XBB.1.5, are necessary to help people keep track of and communicate about the strains. A WHO spokesperson said the unofficial names are not necessary, because different omicron sublineages should not require different mitigation measures among the public. 


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