Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States - World Health Organization HQ, 28 November 2021 (updated 29 November with minor editorial corrections)

Overview

• On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC), on the basis of advice from WHO’s Technical Advisory Group on Virus Evolution. The variant has been given the name Omicron.

• Omicron is a highly divergent variant with a high number of mutations, including 26-32 in the spike, some of which are concerning and may be associated with immune escape potential and higher transmissibility. However, there are still considerable uncertainties.

• The main uncertainties are (1) how transmissible the variant is and whether any increases are related to immune escape, intrinsic increased transmissibility, or both; (2) how well vaccines protect against infection, transmission, clinical disease of different degrees of severity and death; and (3) does the variant present with a different severity profile.

• Public health advice is based on current information and will be tailored as more evidence emerges around those key questions.