WHO updates information on Omicron

Dec. 13, 2021

Cases of Omicron, the new SARS-COV-2 variant, have been identified in 63 countries, according to the World Health Organization (WHO), which issued a technical brief with updated information about the variant.

The WHO designated Omicron (B.1.1.529) as a variant of concern in November. In the technical brief, the WHO provided updated information on Omicron’s rate of transmission, severity of cases, potential to evade vaccines, and its impact on diagnostic testing and therapeutics.

Omicron has a high number of mutations, including 26-32 in the spike protein, and based on limited evidence, it may spread faster than Delta, the WHO said. “It is spreading faster than the Delta variant in South Africa where Delta circulation was low, but also appears to spread more quickly than the Delta variant in other countries where the incidence of Delta is high, such as in the United Kingdom. Whether Omicron’s observed rapid growth rate in countries with high levels of population immunity is related to immune evasion, intrinsic increased transmissibility, or a combination of both remains uncertain. However, given the current available data, it is likely that Omicron will outpace the Delta variant where community transmission occurs,” the WHO said.

The WHO also said preliminary evidence suggests that Omicron may produce milder disease than Delta. But also said that “more data are needed to understand the severity profile.”

As far as vaccine efficacy, the WHO said, “there are limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness to date for Omicron. Preliminary evidence, and the considerably altered antigenic profile of the Omicron spike protein, suggests a reduction in vaccine efficacy against infection and transmission associated with Omicron. There is some preliminary evidence that the incidence of reinfection has increased in South Africa, which may be associated with humoral (antibody-mediated) immune evasion. In addition, preliminary evidence from a few studies of limited sample size have shown that sera obtained from vaccinated and previously infected individuals had lower neutralization activity (the size of the reduction ranges considerably) than with any other circulating VOCs of SARS-CoV-2 and the ancestral strain.”

However, “the diagnostic accuracy of routinely used PCR and antigen-based rapid diagnostic test (Ag-RDT) assays does not appear to be influenced by Omicron. Most Omicron variant sequences reported include a deletion in the S gene, causing some S gene targeting PCR assays to appear negative. Although some publicly shared sequences lack this deletion, this remains a minority of currently available sequences, and S gene target failure (SGTF) can, therefore, be used as a useful proxy marker of Omicron, for surveillance purposes. However, confirmation should be obtained by sequencing, as this deletion can also be found in other VOCs (e.g., Alpha and subsets of Gamma and Delta).”

Likewise, many therapeutics should not be impacted by Omicron. Therapies that target “the host responses (such as corticosteroids, and interleukin 6 receptor blockers and prophylaxis with anticoagulation) are expected to remain effective. However, monoclonal antibodies will need to be tested individually, for their antigen binding and virus neutralization and these studies should be prioritized.”

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