The Omicron viruses account for over 98% of the publicly available sequences since February 2022 and constitute the genetic background from which new SARS-CoV-2 variants will likely emerge, although the emergence of variants derived from previously circulating VOCs or of completely new variants remains possible. The previous system classified all Omicron sublineages as part of the Omicron VOC and thus did not have the granularity needed to compare new descendent lineages with altered phenotypes to the Omicron parent lineages (BA.1, BA.2, BA.4/BA.5). Therefore, from 15 March 2023, the WHO variant tracking system will consider the classification of Omicron sublineages independently as variants under monitoring (VUMs), VOIs, or VOCs.
WHO is also updating the working definitions for VOCs and VOIs. The main update consists in making the VOC definition more specific, to include major SARS-CoV-2 evolutionary steps that require major public health interventions. For the updated definitions, please visit the WHO variant tracking website.
In addition, going forward, WHO will assign Greek labels for VOCs, and will no longer do so for VOIs.
Source: Statement on the update of WHO’s working definitions and tracking system for SARS-CoV-2 variants of concern and variants of interest