Emergence and Spread of SARS-CoV-2 Variants of Concern in Canada: a Retrospective Analysis from Clinical and Wastewater Data

The spread of SARS-CoV-2 has been studied at unprecedented levels worldwide. In jurisdictions where molecular analysis was performed on large scales, the emergence and competition of numerous SARS-CoV-2 lineages has been observed in near real-time. Lineage identification, traditionally performed from clinical samples, can also be determined by sampling wastewater from sewersheds serving populations of interest. Of particular interest are variants of concern (VOCs), SARS-CoV-2 lineages that are associated with increased transmissibility and/or severity. Here, we consider clinical and wastewater data sources to retrospectively assess the emergence and spread of different VOCs in Canada. We show that, overall, wastewater-based VOC identification provides similar insights to the surveillance based on clinical samples. Based on clinical data, we observed a synchrony in VOC introduction as well as similar emergence speeds across most Canadian provinces despite the large geographical size of the country and differences in provincial public health measures. In particular, it took approximately four months for VOC Alpha and Delta to contribute to half of the incidence, whereas VOC Omicron achieved the same contribution in less than one month. By quantifying the timing and rapidity of SARS-CoV-2 VOCs invasion in Canada, this study provides important benchmarks to support preparedness for future VOCs, and to some extent, for future pandemics caused by other pathogens.