![]() ![]() Immune escape: Omicron is better at causing breakthrough infections in vaccinated people than Delta, and can evade neutralization by prior infection or vaccine-acquired antibodies.Many factors likely contribute to the growth advantage of Omicron. ![]() ![]() Initial evidence indicates BA.2 may be more transmissible than BA.1, based on the growth of BA.2 in Denmark and the UK, and indications of a higher SAR than other Omicron lineages. Higher household secondary attack rates (SAR) have been observed for Omicron compared with Delta in the UK and Denmark and very high SAR have been observed in some settings such as gatherings, and parties, including among vaccinated people. Understanding increased transmissibilityĭata from South Africa and modelling from the UK estimate Omicron to be 3.05 and 5.57 times more transmissible, respectively, than the Delta variant. For example, further surveillance of zoonotic reservoirs of SARS-CoV-2 in animals (e.g., mink, white-tailed deer, hamsters, etc.), could improve understanding of SARS-CoV-2 evolution. Understanding the origins will be important to identifying where future variants may arise. Omicron may have emerged from any of these hypotheses, or a combination of them, but the divergence from the original strain may have occurred more than a year ago. (3) zoonotic spillover infection from humans to an animal host where the virus evolved and subsequently spilled back into the human population. (2) chronic COVID-19 infection of an immunosuppressed person over an extended period leading to evolution of the virus within a single person (1) early divergence from the original strain and parallel evolution in a population with poor surveillance and sequencing, where the variant went undetected There are three possible scenarios that may have given rise to Omicron. An Omicron sublineage, BA.1.1 has also emerged in Canada and elsewhere in the world. The BA.1 and BA.2 lineages share 32 common mutations, but each has 19 unique mutations. Omicron has multiple lineages (BA.1, BA.2, and BA.3), all of which arose during the same period. Omicron does not appear to have evolved directly from any known variant, and has more than 50 mutations compared with original strain of the virus, including more than 30 on the spike protein. Omicron (B.1.1.529) was first designated a Variant of Concern (VOC) by Canada on November 28, 2021, based on evidence of increased transmissibility, increased risk of infection, and reduced vaccine effectiveness. Moving in the shadows – the origins of Omicron This blog provides an update on what we know about the Omicron variant, which may be important to continuing to manage the current wave and prepare for future variants. Others – including some Canadian provinces – are likely past their peak and have started reducing or removing COVID-related restrictions. Some countries have yet to reach the peak of their Omicron wave. Omicron has now been detected in all regions of the world, including those with more stringent exposure control and containment strategies for COVID-19. Since our last blog at the beginning of the Omicron wave, we have learned more about transmissibility, severity, and the effect of vaccination. ![]()
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