OBJECTIVES: Despite high vaccination rates, COVID-19 continues to be associated with substantial burden among immunocompromised patients globally. This study aimed to describe and compare outcomes during and following COVID-19 hospitalizations among immunocompromised and non-immunocompromised patients.

METHODS: We used Ontario’s population-based health administrative databases to identify COVID-19 hospitalizations and associated outcomes between 01/2020 and 03/2023. Immunocompromised patients included those with ≥1 of: solid organ or stem cell transplant; hematological malignancy; rheumatoid arthritis; multiple sclerosis; or primary immunodeficiency. Non-immunocompromised patients were matched 4:1 to immunocompromised patients on age, sex, and time of admission. Clinical burden, healthcare resource use, and costs were assessed during hospitalization and post-discharge. Relative risks (RRi), relative rates (RRa) and corresponding 95% confidence intervals (CIs) were estimated using log-binomial or modified Poisson regression. Relative mean (95% CI) differences in costs were estimated using gamma regression. All estimates accounted for neighbourhood deprivation, long-term care residency, baseline comorbidities, and COVID-19 vaccination status.

RESULTS: 9,283 eligible immunocompromised patients hospitalized with COVID-19 (mean age 68.7 years; 52.1% female) were matched to 37,127 non-immunocompromised patients. During index hospitalization, immunocompromised patients had greater risk of admission to intensive care units (RRi 1.06[1.01-1.12]), receipt of ventilation (RRi 1.27[1.19-1.36]), and all-cause mortality (RRi 1.34[1.27-1.41]) compared to non-immunocompromised patients. Within 30-days post-discharge, immunocompromised patients had greater rates of all-cause readmission to hospital (RRa 1.33[1.26-1.40]), admission to emergency departments (RRa 1.13[1.08-1.18]), home oxygen use (RRi 1.35[1.15-1.58]), and COVID-19-related rehabilitation (RRa 1.52[1.22-1.89]). This amounted to 21%[16%-25%] and 51%[45%-58%] greater costs associated with care of immunocompromised patients in hospital and post-discharge respectively. Within 180 days post-discharge, rates of resource use remained elevated for immunocompromised patients with 57%[50%-64%] greater costs of care.

CONCLUSIONS: Immunocompromised patients experienced more severe COVID-19 outcomes in hospital and post-discharge in comparison to non-immunocompromised patients. COVID-mitigating policies and prophylactic treatments are needed to continue to protect immunocompromised populations.