WHO has updated its tracking system and working definitions for variants of SARS-CoV-2, the virus that causes COVID-19, to better reflect the current global variant landscape, to independently evaluate Omicron sublines in circulation and identify new variants to classify more clearly when necessary.
SARS-CoV-2 continues to evolve. Since the onset of the COVID-19 pandemic, multiple variants of concern (VOCs) and variants of interest (VOIs) have been designated by the WHO, based on their estimated potential for expansion and replacement of previous variants, for causing new waves of increased circulation , and for the need to adapt public health measures.
Based on comparisons of antigenic cross-reactivity using animal sera, replication studies in experimental models of the human respiratory tract, and evidence from human clinical and epidemiological studies, there is consensus among experts in the WHO Technical Advisory Group on the evolution of SARS-CoV -2 viruses (TAG-VE) which, compared to previous Omicron variants, represents the most diverse VOCs observed to date. Since its emergence, Omicron viruses have continued to evolve genetically and antigenically with a growing array of sublines, all of which have thus far been characterized by evasion properties of existing population immunity and a preference to infect the upper respiratory tract (vs. lower respiratory tract). , compared to pre-Omicron VOCs.
The Omicron viruses account for more than 98% of the publicly available sequences as of February 2022 and are the genetic background from which new SARS-CoV-2 variants are likely to arise, although the emergence of variants derived from previously circulating VOCs or of completely new variants remains possible. The previous system classified all Omicron sublines as part of the Omicron VOC and thus lacked the granularity needed to compare new descendants with altered phenotypes to the Omicron parent lines (BA.1, BA.2, BA.4/BA .5). Therefore, from March 15, 2023, the WHO Variant Tracking System will independently consider the classification of Omicron sublines as variants under monitoring (VUMs), VOIs or VOCs.
The WHO is also updating the working definitions for VOCs and VOIs. The main update consists of making the VOC definition more specific, to include key SARS-CoV-2 evolutionary steps that require major public health interventions. For the updated definitions, visit the WHO variant tracking website.
In addition, the WHO will in the future assign Greek labels to VOCs, and no longer to VOIs.
Taking these changes into account, Alpha, Beta, Gamma, Delta and the Omicron parent line (B.1.1.529) are considered formerly circulating VOCs. The WHO has now classified XBB.1.5 as a VOI.
The WHO will also continue to issue regular risk assessments for both VOIs and VOCs (see the latest risk assessment for XBB.1.5).
The WHO emphasizes that these changes do not mean that the circulation of Omicron viruses no longer poses a threat to public health. The changes were made earlier to better identify additional or new threats beyond those of the current Omicron viruses in circulation.