Outcomes and characteristics of patients hospitalized for COVID-19 in British Columbia, Ontario and Quebec during the Omicron wave.

Background: Omicron is the current predominant variant of concern of SARS-CoV-2. We hypothesized that vaccination alters outcomes of patients hospitalized with COVID-19 during the Omicron wave and that these patients have different characteristics and outcomes than in previous waves.
Methods: This is a substudy of the Host Response Mediators in Coronavirus (COVID-19) Infection (ARBs CORONA I) trial, which included adults admitted to hospital with acute COVID-19 up to July 2022 from 9 hospitals in British Columbia, Ontario and Quebec. We excluded emergency department visits without hospital admission, readmissions and admissions for another reason. Using adjusted regression analysis, we compared mortality and organ dysfunction between vaccinated (≥ 2 doses) and unvaccinated patients during the Omicron wave, as well as between all patients in the Omicron and first 3 waves of the COVID-19 pandemic.
Results: During the Omicron wave, 28-day mortality was significantly lower in vaccinated ( n = 19/237) than unvaccinated hospitalized patients ( n = 12/127) (adjusted odds ratio [OR] 0.36, 95% confidence interval [CI] 0.15-0.89); vaccinated patients had lower risk of admission to the intensive care unit, invasive ventilation and acute respiratory distress syndrome and shorter hospital length of stay. Patients hospitalized during the Omicron wave had more comorbidities than in previous waves, and lower 28-day mortality than in waves 1 and 2 (adjusted OR 0.38, 95% CI 0.24-0.59; and 0.42, 95% CI 0.26-0.65) but not wave 3 (adjusted OR 0.81, 95% CI 0.43-1.51) and had less organ dysfunction than in the first 2 waves.
Interpretation: Patients who were at least double vaccinated had lower mortality than unvaccinated patients hospitalized during the Omicron wave. Patients hospitalized during the Omicron wave had more chronic disease and lower mortality than in the first 2 waves, but not wave 3. Changes in vaccination, treatments and predominant SARS-CoV-2 variant may have decreased mortality in patients hospitalized during the Omicron wave.
Competing Interests: Competing interests: Keith Walley reports receiving a Canadian Institutes of Health Research (CIHR) Foundation grant, paid to the University of British Columbia. Dr. Walley has also participated on data safety monitoring boards (unpaid) for Northern Therapeutics and the Cellular Immuno-Therapy for COVID-19 Acute Respiratory Distress Syndrome (CIRCA-19) trial. Allison McGeer reports receiving grants from Sanofi, Merck and Pfizer (paid to institution), as well as payment or honoraria from AstraZeneca, Merck, Biogen and Moderna. Dr. McGeer has also received travel support from Moderna and has participated on a data safety monitoring or advisory board for Pfizer, GlaxoSmithKline, Moderna, Medicago, Janssen, AstraZeneca, Novavax and Sanofi.
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