From https://metaculus.com/questions/15656/new-sars-cov-2-variant-of-concern-before-2024/

On 15/16 March 2023, the WHO updated its tracking system and working definitions for SARS-CoV-2 Variants of Concern to take to account for the dominance and variance of the Omicron variant and its sublineages. The new definitions mean that Omicron sublineages will be considered independently as Variants under Monitoring, Variants of Interest, or Variants of Concern. As a result of these changes, the Omicron subvariant XBB.1.5 was classified as a Variant of Interest.

The emergence of new variants has been associated with COVID-19 case and hospitalization surges, and with the efficacy of treatments and vaccinations.