The WHO’s Evolving Framework for VOCs and VOIs: Implications for COVID-19 Control
The World Health Organization (WHO) has announced updates to its tracking system and working definitions for variants of SARS-CoV-2, the virus that causes COVID-19. These updates have been implemented to more accurately correspond to the current global variant landscape, independently evaluate Omicron sublineages in circulation, and classify new variants more clearly when required.
The COVID-19 pandemic has seen the emergence of multiple variants of concern (VOCs) and variants of interest (VOIs), which have been designated by the WHO based on their assessed potential for expansion and replacement of prior variants, causing new waves with increased circulation, and the need for adjustments to public health actions. Since its emergence, Omicron has represented the most divergent VOC seen to date. The virus has continued to evolve genetically and antigenically with an expanding range of sublineages. These sublineages have all been characterized by properties of evasion of existing population immunity and a preference to infect the upper respiratory tract.
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. The previous tracking 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. 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.
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 major SARS-CoV-2 evolutionary steps that require major public health interventions. The updated definitions can be found on the WHO variant tracking website. Going forward, the 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. The WHO has now classified XBB.1.5 as a VOI. The organization will also continue to issue regular risk assessments for both VOIs and VOCs.
The 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 to better identify additional or new threats over and above those posed by the current Omicron viruses in circulation.
The updates to the WHO tracking system and working definitions are critical in identifying and tracking new variants of SARS-CoV-2, allowing public health officials to stay ahead of the virus and implement necessary measures to protect the population. The organization’s Technical Advisory Group on SARS-CoV-2 Virus Evolution has been instrumental in providing expert advice and guiding the WHO’s efforts in this area.
It is important to note that even with these updates, the fight against COVID-19 is far from over. It is crucial that individuals continue to follow public health guidelines, such as wearing masks, practicing social distancing, and getting vaccinated. These measures remain our best defense against the spread of the virus and the emergence of new variants.
In conclusion, the WHO’s updates to its tracking system and working definitions for variants of SARS-CoV-2 are a significant step forward in the global fight against COVID-19. By better identifying and tracking new variants, public health officials can take necessary measures to protect the population. However, it is important to remember that our best defense against the spread of the virus remains practicing public health guidelines and getting vaccinated.
