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Pandemian tilanne globaaleina käyrinä
Statement on the update of WHO’s working definitions and tracking system for SARS-CoV-2 variants of concern and variants of interest
WHO has updated its tracking system and working definitions for
variants of SARS-CoV-2, the virus that causes COVID-19, to better
correspond to the current global variant landscape, to independently
evaluate Omicron sublineages in circulation, and classify new variants
more clearly when required.
SARS-CoV-2 continues to evolve.
Since the beginning of the COVID-19 pandemic, multiple variants of
concern (VOCs) and variants of interest (VOIs) have been designated by
WHO based on their assessed potential for expansion and replacement of
prior variants, for causing new waves with increased circulation, and
for the need for adjustments to 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 experts in WHO’s Technical Advisory Group on
SARS-CoV-2 Virus Evolution (TAG-VE) that compared to previous variants,
Omicron represents the most divergent VOC seen to date. Since its
emergence, Omicron viruses have continued to evolve genetically and
antigenically with an expanding range of sublineages, which so far have
all been characterized by properties of evasion of existing population
immunity and a preference to infect the upper respiratory tract (versus
lower respiratory tract), as compared to pre-Omicron VOCs.
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.
With these changes factored in, Alpha, Beta, Gamma, Delta as well as the Omicron parent lineage (B.1.1.529) are considered previously circulating VOCs. 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 latest risk assessment for XBB.1.5).
WHO emphasizes that these changes do not imply that the circulation of Omicron viruses no longer pose a threat to public health. Rather, the changes have been made in order to better identify additional or new threats over and above those posed by the current Omicron viruses in circulation.
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