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Estimates of SARS-CoV-2 Omicron Variant Severity in Ontario, Canada

Educational Objective
To identify the key insights or developments described in this article

The World Health Organization designated Omicron as a variant of concern on November 26, 2021. Omicron has 37 mutations in the spike protein and has rapidly replaced Delta as the dominant variant globally, due to increased immune evasion.1 It is less clear how the severity of Omicron compares with that of Delta. Early data from South Africa suggest that Omicron may be less severe than prior lineages2; however, the low average age of infected individuals, extent of previous infection, and low vaccination rates affect generalizability to certain other countries. In Ontario, Canada, we examined hospitalizations and deaths associated with Omicron compared with matched patients infected with Delta.

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Article Information

Accepted for Publication: February 4, 2022.

Published Online: February 17, 2022. doi:10.1001/jama.2022.2274

Corresponding Author: Kevin A. Brown, PhD, Public Health Ontario, 480 University Ave, Suite 300, Toronto, ON M5G1V2, Canada (kevin.brown@oahpp.ca).

Author Contributions: Ms Ulloa and Dr Brown had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: All authors.

Acquisition, analysis, or interpretation of data: Ulloa, Brown.

Drafting of the manuscript: All authors.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Ulloa, Brown.

Administrative, technical, or material support: Brown.

Supervision: Brown.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was supported by Public Health Ontario; the authors received no external funding for the conduct of this study.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

References
1.
Mannar  D , Saville  JW , Zhu  X ,  et al.  SARS-CoV-2 Omicron variant: antibody evasion and cryo-EM structure of spike protein-ACE2 complex.   Science. Published January 20, 2022. doi:10.1126/science.abn7760PubMedGoogle Scholar
2.
Maslo  C , Friedland  R , Toubkin  M , Laubscher  A , Akaloo  T , Kama  B .  Characteristics and outcomes of hospitalized patients in South Africa during the COVID-19 Omicron wave compared with previous waves.   JAMA. 2022;327(6):583-584. doi:10.1001/jama.2021.24868PubMedGoogle ScholarCrossref
3.
Public Health Ontario. Early dynamics of Omicron in Ontario, November 1 to December 16, 2021. Accessed December 24, 2021. https://www.publichealthontario.ca/-/media/documents/ncov/epi/covid-19-early-dynamics-omicron-ontario-epi-summary.pdf
4.
Wolter  N , Jassat  W , Walaza  S ,  et al.  Early assessment of the clinical severity of the SARS-CoV-2 omicron variant in South Africa: a data linkage study.   Lancet. 2022;399(10323):437-446. doi:10.1016/S0140-6736(22)00017-4PubMedGoogle ScholarCrossref
5.
Sheikh  A , Kerr  S , Woolhouse  M , McMenamin  J , Robertson  C . Severity of Omicron variant of concern and vaccine effectiveness against symptomatic disease: national cohort with nested test negative design study in Scotland. University of Edinburgh. Published December 22, 2021. Accessed February 11, 2022. https://www.research.ed.ac.uk/en/publications/severity-of-omicron-variant-of-concern-and-vaccine-effectiveness-
6.
Ferguson  N , Ghani  A , Hinsley  W , Volz  E ; Imperial College COVID-19 Response Team.  Report 50: Hospitalisation Risk for Omicron Cases in England. Imperial College London; 2021. doi:10.25561/93035
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