WHO declares Omicron as variant of concern? It was 26 November 2021 that WHO declared that the world was facing a new variant of concern: Omicron.21K (omicron) is of primarily concern because of the detection of large number of mutation in its spike gene Figure 1. Most of these variants plays an important role in antibody recognition and ACE2 binding and are in the N-terminal or receptor-binding domain.