#16,409
Despite the headache-inducing shouting match on the Internet between those who think Omicron is a toothless, incredibly mild variant that will quickly end the pandemic - and those who see it as a super-transmissible juggernaut that will overwhelm society - the ultimate impact of B.1.1.529 remains unclear.
South Africa has a relatively young population, and - unlike most of the rest of the world - hosted a major wave of the Beta variant in 2020. It is unknown how (or even if) that may be affecting the impact of Omicron in South Africa today (see Science: Heterologous Infection and Vaccination Shapes Immunity Against SARS-CoV-2 Variants).While I see some hopeful signs on the severity front - at least based on early reports out of South Africa - it is far too soon to know how that will translate to the rest of the world.
The standard 2-dose COVID vaccine regimen appears insufficient for preventing symptomatic infection (although it may lessen severity), and prior infection with earlier variants appears to provide little protection as well.The one thing that everyone seems to agree on is that Omicron is spreading much faster than previous COVID variants, and that immune escape appears to play a major role.
Even if we assume Omicron is very mild, there are no guarantees that it will be the last variant we will have to deal with (see Proposal to split B.1.1.529 to incorporate a newly characterised sibling lineage on CoV-Lineages).Booster shots - at least in the short run - appear to provide reasonable protection (70%-75%) against symptomatic infection. How long that lasts remains to be seen.
Because of these uncertainties, many countries are acting aggressively to prepare for Omicron's arrival.
On Friday the WHO updated their Nov 29th guidance, issuing a 16-page Technical Brief for Member states. I've reproduced the link, overview, and a couple of excerpts below.Is it possible they are overreacting? Sure. But they won't know how big of an impact this variant will have for weeks, and by that time, it will be too late to act.
Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States
10 December 2021 | Technical document
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 variant is a highly divergent variant with a high number of mutations, including 26-32 in the spike protein, some of which are concerning and may be associated with immune escape potential and higher transmissibility. However, there are still considerable uncertainties. As of 9 December 2021, cases of human infections with this variant have been identified in 63 countries across all six WHO regions. Current understanding of the Omicron variant from recent data are likely to evolve as more data becomes available.
- The overall threat posed by Omicron largely depends on three key questions, including: (1) how transmissible the variant is; (2) how well vaccines and prior infection protect against infection, transmission, clinical disease and death; and (3) how virulent the variant is compared to other variants. Public health advice is based on current information and will be tailored as more evidence emerges around those key questions.
- Based on current limited 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 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.
- 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 in the EU/EEA to date have been mild or asymptomatic, it remains unclear to what extent Omicron may be inherently less virulent. More data are needed to understand the severity profile.
- 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.
- 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).
- Therapeutic interventions for the management of patients with severe or critical COVID-19 associated with the Omicron variant that target 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.
The following is the WHO's Global Risk Assessment as of December 10th on the Omicron variant.
Global risk assessment
This section summarizes the evidence presented above to arrive at an overall global risk assessment for the Omicron variant.
- At present, a total of 63 countries have identified Omicron cases in all six WHO regions.
- Omicron is spreading fast in South Africa, where the incidence of Delta is low, but also appears to be spreading faster than the Delta variant in other countries with high incidence of Delta circulation, suggesting that Omicron will likely outpace the Delta variant where community transmission occurs.
- The clinical severity of Omicron remains uncertain, but increased transmission, with similar or even lower severity than Delta could pose overwhelming demands on health care systems and lead to significant morbidity. The impact on vulnerable populations would be substantial, particularly in countries with low vaccination coverage.
- Preliminary evidence from epidemiological studies on reinfection, neutralization studies, modelling estimates, and the considerably altered antigenic profile of the Omicron spike protein, suggests some degree of humoral immune evasion and a likely reduction in vaccine efficacy and effectiveness against infection and transmission associated with Omicron.
- The overall risk related to the new variant of concern Omicron thus remains very high for a number of reasons. First, the global risk of COVID-19 remains very high overall, and second, there is concerning preliminary evidence on Omicron suggesting both potential immune escape and higher transmissibility that could lead to further surges with severe consequences. Our understanding is still evolving, and the risk assessment will be updated as more information becomes available.
While we all hope that Omicron proves to be far less disruptive than Delta, public health officials - unlike internet pundits - don't have the luxury of being able to assume that to be true.
