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Clinical severity of Omicron subvariants BA.1, BA.2, and BA.5 in a population-based cohort study in British Columbia,Canada |
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| Authors: | Shannon L. Russell Braeden R. A. Klaver Sean P. Harrigan Kimia Kamelian John Tyson Linda Hoang Marsha Taylor Beate Sander Sharmistha Mishra Natalie Prystajecky Naveed Z. Janjua James E. A. Zlosnik Hind Sbihi |
| Affiliation: | 1. British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada;2. British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada;3. Public Health Agency of Canada, National Microbiology Laboratory, Winnipeg, Manitoba, Canada;4. Institute of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada Public Health Ontario, Toronto, Ontario, Canada;5. Institute of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada MAP-Centre for Urban Health Solutions, St. Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada |
| Abstract: | The SARS-CoV-2 variant Omicron emerged in late 2021. In British Columbia (BC), Canada, and globally, three genetically distinct subvariants of Omicron, BA.1, BA.2, and BA.5, emerged and became dominant successively within an 8-month period. SARS-CoV-2 subvariants continue to circulate in the population, acquiring new mutations that have the potential to alter infectivity, immunity, and disease severity. Here, we report a propensity-matched severity analysis from residents of BC over the course of the Omicron wave, including 39,237 individuals infected with BA.1, BA.2, or BA.5 based on paired high-quality sequence data and linked to comprehensive clinical outcomes data between December 23, 2021 and August 31, 2022. Relative to BA.1, BA.2 cases were associated with a 15% and 28% lower risk of hospitalization and intensive care unit (ICU) admission (aHRhospital = 1.17; 95% confidence interval [CI] = 1.096–1.252; aHRICU = 1.368; 95% CI = 1.152–1.624), whereas BA.5 infections were associated with an 18% higher risk of hospitalization (aHRhospital = 1.18; 95% CI = 1.133–1.224) after accounting for age, sex, comorbidities, vaccination status, geography, and social determinants of health. Phylogenetic analysis revealed no specific subclades associated with more severe clinical outcomes for any Omicron subvariant. In summary, BA.1, BA.2, and BA.5 subvariants were associated with differences in clinical severity, emphasizing how variant-specific monitoring programs remain critical components of patient and population-level public health responses as the pandemic continues. |
| Keywords: | COVID-19 hospitalization intensive care unit phylogeny variant of concern whole genome sequencing |