Observational studyCMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne2021
Evaluation of the relative virulence of novel SARS-CoV-2 variants: a retrospective cohort study in Ontario, Canada.
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Who cites it
190 citing papers in PubMed, 4 syntheses or guidelines pooled it.
- Clinical Severity of SARS-CoV-2 Variants during COVID-19 Vaccination: A Systematic Review and Meta-Analysis.Viruses · 2023Pooled it
- COVID-19 Convalescent Plasma for the Treatment of Immunocompromised Patients: A Systematic Review and Meta-analysis.JAMA network open · 2023Pooled it
- Pooled it
- The Disease Severity and Clinical Outcomes of the SARS-CoV-2 Variants of Concern.Frontiers in public health · 2021Pooled it
- Article
- Combinatorial analysis of clinical and genomic data used to assess the association between SARS-CoV-2 mutations and disease severity.PNAS nexus · 2026Article
- Healthcare-associated COVID-19 in Ontario, Canada: case classification and relative mortality.BMC infectious diseases · 2026Article
- Psychiatric and Neurological Involvement in COVID-19 Hospitalized Patients Through the Global Pandemic in Central Romania.Journal of clinical medicine · 2026Article
- A public health perspective of SARS-CoV-2 evolution and surveillance strategies in Germany from 2020 to 2023.Communications medicine · 2025Review
- Derivation and validation of a point-based forecasting tool for SARS-CoV-2 critical care occupancy: a population-based modeling study.Lancet regional health. Americas · 2025Article
- The implementation and evaluation of the Ontario COVID@Home Clinical Primary Care Pathway.Family practice · 2025Article
- The Impact of Vaccination Frequency on COVID-19 Public Health Outcomes: A Model-Based Analysis.Vaccines · 2025Article
- Scaling COVID-19 rates with population size in the United States.Journal of the Royal Society, Interface · 2025Article
- Metabolic syndrome enhances SARS-CoV-2 disease severity and reduces mRNA vaccine efficacy in a mouse model.bioRxiv : the preprint server for biology · 2025Article
- Article
- Article
- Burden of SARS-CoV-2 infection and severe illness in South Africa (March 2020-August 2022): a synthesis of epidemiological data.BMJ public health · 2025Article
- Methodology for predicting hospital admissions and evaluating recovery rates for coronavirus disease in Japan.PloS one · 2025Article
- Differential Impact of Spike Protein Mutations on SARS-CoV-2 Infectivity and Immune Evasion: Insights from Delta and Kappa Variants.Journal of microbiology and biotechnology · 2024Article
- The optimal spatially-dependent control measures to effectively and economically eliminate emerging infectious diseases.PLoS computational biology · 2024Article
130 more citing papers are in PubMed but not listed here.
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2 authors.
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No grant is acknowledged in the PubMed record.
Abstract
backgroundBetween February and June 2021, the initial wild-type strains of SARS-CoV-2 were supplanted in Ontario, Canada, by new variants of concern (VOCs), first those with the N501Y mutation (i.e., Alpha/B1.1.17, Beta/B.1.351 and Gamma/P.1 variants) and then the Delta/B.1.617 variant. The increased transmissibility of these VOCs has been documented, but knowledge about their virulence is limited. We used Ontario's COVID-19 case data to evaluate the virulence of these VOCs compared with non-VOC SARS-CoV-2 strains, as measured by risk of hospitalization, intensive care unit (ICU) admission and death.
methodsWe created a retrospective cohort of people in Ontario who tested positive for SARS-CoV-2 and were screened for VOCs, with dates of test report between Feb. 7 and June 27, 2021. We constructed mixed-effect logistic regression models with hospitalization, ICU admission and death as outcome variables. We adjusted models for age, sex, time, vaccination status, comorbidities and pregnancy status. We included health units as random intercepts.
resultsOur cohort included 212 326 people. Compared with non-VOC SARS-CoV-2 strains, the adjusted elevation in risk associated with N501Y-positive variants was 52% (95% confidence interval [CI] 42%-63%) for hospitalization, 89% (95% CI 67%-117%) for ICU admission and 51% (95% CI 30%-78%) for death. Increased risk with the Delta variant was more pronounced at 108% (95% CI 78%-140%) for hospitalization, 235% (95% CI 160%-331%) for ICU admission and 133% (95% CI 54%-231%) for death.
interpretationThe increasing virulence of SARS-CoV-2 VOCs will lead to a considerably larger, and more deadly, pandemic than would have occurred in the absence of the emergence of VOCs.
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