Comparison of severity of immunized versus non-immunized COVID-19 patients admitted to ICU: A prospective observational study

Background: Vaccines against COVID-19 show high efficacy, yet, infection is still being detected among immunized patients, although with blunted severity. The purpose of this study was to assess the severity of COVID-19 infection among immunized versus non-immunized COVID-19 patients admitted to ICU. Method: A prospective observational cohort study, including all COVID-19 patients admitted to intensive care unit between January 1st, 2021 and June 30th, 2021 were eligible for inclusion. A comparison of severity upon hospitalization of immunized versus non-immunized patients on a 7-level ordinal scale was conducted, using ordinal logistic regression. Results: 592 patients were enrolled, 524 (88.5%) non-immunized, 63 (10.6%) partially immunized, and 5 (0.9%) fully immunized, partially and fully immunized patients were grouped together. Majority of immunized patients (86.7%) were symptomatic before 21 days of immunization. Non-immunized group had fewer patients in the lower severity categories, while more patients in the higher severity categories compared to immunized group. At least one dose of immunization was associated with reduction of odds of moving up severity scale (OR = 0.2 [95% CI: 0.15-0.4]; p < 0.001) in a well fitted ordinal logistic regression model. At least one dose of immunization was associated with lower adjusted odds of 30 day all-cause mortality (OR = 0.45 [95% CI: 0.23-0.89]; p = 0.02). Non-immunized group had higher mortality rate (43.9% versus 29.4% [95% CI: 1.5 to 25.8]; p = 0.02). Conclusion: Most COVID-19 patients admitted to ICU were non-immunized, most of the partially immunized patients got infected before immunity could develop, and fully immunized patients were likely non-responders. At least one dose of immunization significantly decreases severity of the disease across all ordinal severity categories, and is significantly associated with lower 30 day all-cause mortality. Accordingly, immunization status may have to be considered when deciding on disposition of COVID-19 patients at the point of triage.