Estimates of SARS-CoV-2 Omicron Variant Severity in Ontario, Canada
Open accessPublished version of a preprint
Abstract
Abstract While it is now evident that Omicron is rapidly replacing Delta, largely due to immune escape, it is less clear how the severity of Omicron compares to Delta. In Ontario, we sought to examine hospitalization and death associated with Omicron, as compared to cases infected with Delta. We conducted a matched cohort study, considering time to hospitalization or death as the outcome. Cases were matched on gender, age, vaccination status, health region and onset date. We identified 29,594 Omicron cases that met eligibility criteria, of which 11,622 could be matched with at least one Delta case (N=14,181). There were 59 (0.51%) hospitalizations and 3 (0.03%) deaths among matched Omicron cases, compared to 221 (1.6%) hospitalizations and 17 (0.12%) deaths among matched Delta cases. The risk of hospitalization or death was 65% lower (hazard ratio, HR=0.35, 95%CI: 0.26, 0.46) among Omicron cases compared to Delta cases, while risk of intensive care unit admission or death was 83% lower (HR=0.17, 95%CI: 0.08, 0.37). While severity is likely to be reduced, the absolute number of hospitalizations and impact on the healthcare system may nevertheless be significant due to the increased transmissibility of Omicron.
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There is a significant reduction in mortality from Omicron infection.
“With the significant reduction in mortality from Omicron infection [37]”
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SARS-CoV-2 Omicron variant: Antibody evasion and cryo-EM structure of spike protein–ACE2 complex
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Heavily mutated Omicron variant puts scientists on alert
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Wong, C. K. H., Au, I. C. H., Lau, K. T. K., Lau, E. H. Y., Cowling, B. J., & Leung, G. M. (2022) · The Lancet · doi:10.1016/s0140-6736(22)01586-0 · Cited by 299 · see citing works
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“With the significant reduction in mortality from Omicron infection [37], the focus of the VE study should shift to protection against more relevant outcomes such as re-infection or post-COVID symptoms.”
- Authors
- Ulloa, A. C., Buchan, S. A., Daneman, N., & Brown, K. A.
- Affiliations
- Public Health Ontario (CA)
- Corresponding author
- Brown, Kevin A.
- Venue
- JAMA
- Publisher
- American Medical Association (AMA)
- Published
- 2022-04-05
- Volume
- 327
- Issue
- 13
- Pages
- 1286
- ISSN
- 0002-9955 (ISSN-L)
- 0098-7484
- PMC
- PMC8855311
- OpenAlex
- W4213069125
- Cited by
- 316
- References
- 6
- Citations by year
- 2026: 6 · 2025: 13 · 2024: 47 · 2023: 110 · 2022: 140
- FWCI
- 37.89
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- JAMA (publishedVersion)
- medRxiv (acceptedVersion, cc-by)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- SARS-CoV-2, Omicron variant, disease severity, COVID-19 pandemic, Ontario
- MeSH terms
- COVID-19, SARS-CoV-2, Humans, Ontario
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