Abstract
While it is now evident that Omicron is rapidly replacing Delta, due to a combination of increased transmissibility and 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 matched cases infected with Delta. We conducted a matched cohort study, considering time to hospitalization or death as the outcome, and analyzed with a Cox proportional hazards model. Cases were matched on age, gender, and onset date, while vaccine doses received and time since vaccination were included as adjustment variables. We identified 6,314 Omicron cases that met eligibility criteria, of which 6,312 could be matched with at least one Delta case (N=8,875) based on age, gender, and onset date. There were 21 (0.3%) hospitalizations and 0 (0%) deaths among matched Omicron cases, compared to 116 (2.2%) hospitalizations and 7 (0.3%) deaths among matched Delta cases. The adjusted risk of hospitalization or death was 54% lower (HR=0.46, 95%CI: 0.27, 0.77) among Omicron cases compared to Delta cases. While severity may be reduced, the absolute number of hospitalizations and impact on the healthcare system could still be significant due to the increased transmissibility of Omicron.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
This study did not receive any external funding.
https://www.medrxiv.org/content/10.1101/2021.12.24.21268382v1
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