Risk Factors for Acquisition of SARS-CoV-2 Among Vaccinated Patients and Healthcare Workers in Hospital Outbreaks: A Case-Control Study

Introduction: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) led to a global health crisis. Despite high vaccination rates, nosocomial SARS-CoV-2 outbreaks persisted at Charité hospital in Berlin, Germany. This doctoral thesis investigated these outbreaks to identify risk and protective factors for vaccinated patients and healthcare workers (HCWs), aiming to improve infection prevention and control (IPC) measures. Methods: We conducted a retrospective case-control study including fully vaccinated Individuals aged 18+ from nosocomial SARS-CoV-2 outbreaks at Charité that were notified in 2022. Data were collected from electronic patients records and questionnaires. Cases tested positive for SARS-CoV-2 ≥ 7 days post-vaccination were matched with controls (1:1). Descriptive analyses and conditional logistic regression analyses were performed for the full cohort and subgroups (patients and HCWs). Results: In total, 538 participants (269 cases and 269 controls) were included (438 patients and 100 HCWs). An immunization more than 3 months ago (OR=1.90, 95% CI: 1.08 - 3.33, p = 0.023) and chemotherapy (OR=4.04, 95% CI: 1.44 - 11.36, p = 0.007) were identified as independent risk factors for SARS-CoV-2 acquisition. In contrast, nat- ural SARS-CoV-2 infection protected from acquiring SARS-CoV-2 (OR=0.21, 95% CI: 0.08 - 0.58, p = 0.002). Subgroup analyses showed that underlying diseases such as congestive heart failure (OR=2.24, 95% CI: 1.05 - 4.77, p = 0.035) and renal disease were associated with SARS-CoV-2 positivity (OR=2.56, 95% CI: 1.00 – 6.51, p = 0.048) for patients. Furthermore, sharing a room with a positive-tested patient (OR=5.88, 95% CI: 2.80 - 12.30, p 3 months ago during outbreaks) to reduce the risk of infection among vaccinated patients and healthcare workers.