On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC) (1), following advice from the WHO’s Technical Advisory Group on Virus Evolution. The variant was given the name Omicron. Omicron is a highly divergent variant with a high number of mutations, including 26-32 mutations in the spike protein, some of which were likely to be associated with humoral immune escape potential and higher transmissibility.
The overall risk related to Omicron remains very high for a number of reasons. First, the global risk of COVID-19 remains very high overall. Second, current data indicate that Omicron has a significant growth advantage over Delta, leading to rapid spread in the community. The rapid increase in cases will lead to an increase in hospitalizations, may pose overwhelming demands on health care systems and lead to significant morbidity, particularly in vulnerable populations.
The overall threat posed by Omicron largely depends on four key questions: (i) how transmissible the variant is; (ii) how well vaccines and prior infection protect against infection, transmission, clinical disease and death; (iii) how virulent the variant is compared to other variants; and (iv) how populations understand these dynamics, perceive risk and follow control measures, including public health and social measures (PHSM). This global risk assessment, and public health advice, are based on the currently best available evidence and will be updated frequently as more information becomes available in relation to these key questions.
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