How big a threat is the Omicron covid variant? WHO shared update

South Africa’s discovery of Omicron – which has a large number of mutations – last month prompted countries around the world to impose travel restrictions on southern African countries and reimpose domestic restrictions to slow its spread.

Highlights of WHO’s ‘Technical Brief and Priority Action for Member States’ released last week:

• As of 9 December 2021, cases of this type of human infection have been identified in 63 countries in all six WHO regions.
• The overall threat posed by Omicron depends largely on three key questions, including: (1) how permeable the version is; (2) how well vaccines and prior infections protect against infection, transmission, clinical disease, and death; and (3) how viral the variant is compared to the other variants.
• Based on limited current evidence, Omicron appears to have a growth advantage over Delta. It is spreading faster than the delta variant in South Africa where delta circulation was low, but appears to spread more quickly than the delta variant in other countries where delta incidence is high, such as in the United Kingdom.
• There are still limited data on the clinical severity of Omicron. While preliminary findings from South Africa suggest it may be less severe than Delta, and all cases reported so far in the EU/EEA are mild or asymptomatic.
• Preliminary evidence, and the significantly altered antigenic profile of the Omicron spike protein, suggests a decreased efficacy of the vaccine against Omicron-associated infections and transmission. There is some preliminary evidence that there is an increased incidence of reinfection in South Africa, which may be linked to humoral (antibody-mediated) immune evasion.
• The diagnostic accuracy of routinely used PCR and antigen-based rapid diagnostic test (Ag-RDT) assays is not affected by Omicron.