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| No images? Click here Friday, 24 December 2021Update on OmicronThe Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States, issued on 23 December, is an update to the last version published on 17 December 2021.Overview On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC), following advice from the 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 mutations in the spike protein, some of which may be associated with humoral immune escape potential and higher transmissibility.As of 22 December 2021, the Omicron variant had been identified in 110 countries across all six WHO Regions. Current understanding of the Omicron variant continues to evolve as more data become available. This technical brief provides updated early evidence on key aspects of Omicron related to transmission, severity and impact on interventions such as diagnostics, therapeutics and vaccines, and outlines a set of priority actions for Member States.The overall threat posed by Omicron largely depends on four key questions: (1) how transmissible the variant is; (2) how well vaccines and prior infection protect against infection, transmission, clinical disease and death; (3) how virulent the variant is compared to other variants; and (4) how populations understand these dynamics, perceive risk and follow control measures, including public health and social measures (PHSM). Public health advice is based on current information and will be tailored as more evidence emerges around those key questions.There is consistent evidence that Omicron has a substantial growth advantage over Delta. It is spreading significantly faster than the Delta variant in countries with documented community transmission, with a doubling time of 2-3 days. Growth rate estimates in South Africa are now declining, driven largely by the declining rates in Gauteng province. It remains uncertain to what extent the observed rapid growth rate since November 2021 can be attributed to immune evasion or intrinsic increased transmissibility, but is likely a combination of both. At the time of writing, estimates of generation times for Omicron are still needed to better understand the observed dynamics. Data on clinical severity of patients infected with Omicron is growing but is still limited. Early data from South Africa, the United Kingdom and Denmark suggest a reduced risk of hospitalization for Omicron compared to Delta. However, the risk of hospitalization is only one aspect of severity, which may be altered by admission practices. More data across different countries are needed to understand how clinical markers of severity – such as the use of oxygen, mechanical ventilation and deaths – are associated with Omicron. At the present time, it is still unclear to what extent the observed reduction in risk of hospitalization can be attributed to immunity from previous infections or vaccination and to what extent Omicron may be less virulent.Preliminary data from several non-peer reviewed studies suggest that there is a reduction in neutralizing titers against Omicron in individuals who have received a primary vaccination series or in those who have had prior SARS-CoV-2 infection. In addition, the increased risk of reinfection reported in England, the United Kingdom , as well as a growing trend of reinfection cases in Denmark and Israel, can be potentially attributed to immune evasion against Omicron. To date, there are still limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness for Omicron. Preliminary findings of vaccine effectiveness studies (test-negative design) have been released from South Africa and the United Kingdom. Available preliminary data should be interpreted with caution because the designs may be subject to selection bias and the results are based on relatively small numbers. Results from the United Kingdom indicate a significant reduction in vaccine effectiveness against symptomatic disease for Omicron compared to Delta after two vaccine doses of either Pfizer BioNTech-Comirnaty or AstraZeneca-Vaxzevria vaccines. There was, however, higher effectiveness two weeks after a Pfizer BioNTech-Comirnaty booster, which was slightly lower or comparable to that against Delta. A non-peer-reviewed study by South African researchers using private health insurance data reported reductions in vaccine effectiveness of the Pfizer BioNTech-Comirnaty vaccine against infection, and to a lesser degree against hospitalization. Details about the methods or results were not available at the time of writing.The diagnostic accuracy of routinely used PCR and antigen-based rapid diagnostic test (Ag-RDT) assays does not appear to be impacted by Omicron; studies of the comparative sensitivity of Ag-RDTs are ongoing. Most Omicron variant sequences reported include a deletion in the S gene, which can cause an S gene target failure (SGTF) in some PCR assays. Although a minority of publicly shared sequences lack this deletion, SGTF can be used as a proxy marker to screen for Omicron. However, confirmation should be obtained by sequencing, since this deletion can also be found in other VOCs (e.g. Alpha and subsets of Gamma and Delta) that are circulating at low frequencies worldwide. Therapeutic interventions for the management of patients with severe or critical Omicron-associated COVID-19 that target host responses (such as corticosteroids, and interleukin 6 receptor blockers) are expected to remain effective. However, preliminary data from non-peer reviewed publications suggest that some of the monoclonal antibodies developed against SARS-CoV-2 may have decreased neutralization against Omicron. Monoclonal antibodies will need to be tested individually for their antigen binding and virus neutralization, and these studies should be prioritized.Previous versions of this Technical Brief are available at the links below. The current version of all WHO information products and publications is authoritative. 17 December 2021 (updated from the last version published on 10 December 2021)10 December 2021 (updated from the last version published on 28 November 2021)28 November 2021 (updated 29 November with minor editorial corrections)Media contacts: You are receiving this NO-REPLY email because you are included on a WHO mail list.
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