In this presentation to the National Advisory Committee on Immunization (NACI) in March 2023, Dr. Sarah Otto summarized recent CAMEO work highlighting how SARS-CoV-2 variants have been evolving in Canada. While BQ.* variant lineages dominated in early 2023, the XBB.1.5 variant has been rising rapidly in frequency and now comprises the majority of COVID-19 cases.
XBB.1.5 is a member of the XBB* family of lineages that arose by recombination from two separate BA.2 lineages (“X” in the start of a lineage name refers to a recombined lineage). Lab studies have shown that the family of BQ.* and XBB* lineages are more immune evasive, but the fast spread of XBB.1.5 is thought to be due to its greater ability to bind to our cells’ ACE2 receptors, leading to higher transmissibility.
At present, Canada-wide immunity is high, so these variants no longer lead to big waves, but they do lead to wavelets and, more importantly, to long term rises in the “sea-level” of COVID-19 cases. Dr. Otto explores models to show how variants are expected to influence future case numbers and how measures that we take can counteract the rising sea-level of COVID-19 (e.g., through vaccinations, improved ventilation, and masking).