Rates of COVID-19-Associated Hospitalization in Immunocompromised Individuals in Omicron-era: A Population-Based Observational Study Using Surveillance Data in British Columbia, Canada

Background People with immune dysfunction have a higher risk for severe COVID-19 outcomes. Omicron variant is associated with a lower rate of hospitalization but higher vaccine escape. This population-based study quantifies COVID-19 hospitalization rate in the Omicron-dominant era among vaccinated people with immune dysfunction, identified as clinically extremely vulnerable (CEV) population before COVID-19 treatment was widely offered. Methods All COVID-19 cases were reported to the British Columbia Centre for Disease Control (BCCDC) between January 7, 2022 and March 14, 2022. Case and population hospitalization rates were estimated across CEV status, age groups and vaccination status. Cumulative rates of hospitalizations for the study period were also compared between CEV and non-CEV individuals matched by sex, age group, region, and vaccination characteristics. Findings A total of 5,591 COVID-19 reported cases and 1,153 hospitalizations among CEV individuals were included. A third vaccine dose with mRNA vaccine offered additional protection against severe illness in CEV individuals. Vaccinated CEV population still had a significantly higher breakthrough hospitalization rate compared with non-CEV individuals. Interpretation CEV population remains a higher risk group and may benefit from additional booster doses and pharmacotherapy. Funding BC Centre for Disease Control and Provincial Health Services Authority ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement BC Centre for Disease Control and Provincial Health Services Authority ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This work was performed under BC Centre for Disease Control (BCCDC)'s mandate to perform population health surveillance and falls under the Behavioral Research Ethics Board at the University of British Columbia (approval # H20-02097) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Data is used for public health surveillance and cannot be shared by the authors. Data access request should be made to the data stewards (BC MOH and PHSA) as per existing processes. R codes for data processing, analysis and visualization can be shared upon request.