WHO has updated its tracking system and working definitions for variants of SARS-CoV-2, the virus that causes COVID-19, to better align with the current global landscape of variants, for independent assessment Omicron sub-lineages in circulation and classify new variants more clearly. when necessary.
SARS-CoV-2 continues to evolve. Since the beginning of the COVID-19 pandemic, WHO has designated multiple Variants of Concern (VOCs) and Variants of Interest (VOIs) based on their assessed potential for expansion and replacement of older variants, to cause new waves with increased circulation, and the need for adjustments in public health actions.
Based on comparisons of antigenic cross-reactivity using animal sera, replication studies in experimental models of the human respiratory tract, and evidence from clinical and epidemiological studies in humans, there is consensus among the experts of the WHO Technical Advisory Group on the Evolution of the SARS-Virus. CoV-2 (TAG-VE) which, compared to previous variants, Omicron represents the most divergent VOC seen to date. Since their appearance, Omicron viruses have continued to evolve genetically and antigenically with an increasing range of sublineages, which have hitherto been characterized by properties of evasion of existing population immunity and a preference for infecting the upper respiratory tract (versus to the lower respiratory tract). , compared to pre-Omicron VOCs.
Omicron viruses account for more than 98% of publicly available sequences as of February 2022 and provide the genetic background from which new SARS-CoV-2 variants are likely to emerge, although variants derived from previously circulating VOCs or from completely new variants. possible. The previous system classified all Omicron sublineages as part of the Omicron VOC and therefore did not have the necessary granularity to compare new descendant lineages with altered phenotypes with the Omicron parent lineages (BA.1, BA.2, BA .4/BA.5). ). Therefore, from March 15, 2023, the WHO Variant Tracking System will consider the classification of Omicron sublineages independently as Variants Under Control (VUM), VOI, or VOC.
The WHO is also updating the working definitions of VOC and VOI. The main update is to make the VOC definition more specific, to include major evolutionary steps in SARS-CoV-2 that require major public health interventions. For up-to-date definitions, visit the WHO variant tracking website.
Also, in the future, WHO will assign Greek labels for VOCs and will no longer do so for VOIs.
Taking these changes into account, Alpha, Beta, Gamma, Delta, as well as the parent line Omicron (B.1.1.529) are considered previously circulating VOCs. The WHO has now classified XBB.1.5 as a VOI.
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 imply that the circulation of Omicron viruses no longer represents a threat to public health. Rather, the changes have been made to better identify new or additional threats beyond those posed by current Omicron viruses in circulation.
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