Statement on the update of WHO's working definitions and tracking system for SARS-CoV-2 variants of concern and variants of interest - World Health Organization

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.

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 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.