Adapted XBB.1.5 vaccine effectiveness against severe COVID-19 outcomes among immunocompromised persons in 2023–24 in six European countries: a VEBIS-EHR network study

BACKGROUND: We estimated the XBB.1.5 vaccine effectiveness (VE) against COVID-19 hospitalization and death in Belgium, Denmark, Italy, Portugal, Spain (Navarre), and Sweden following the 2023-24 fall vaccination campaign among immunocompromised persons (ICPs). RESEARCH DESIGN AND METHODS: We conducted a multi-country retrospective cohort study using electronic health records. Study sites identified ICPs aged ≥18 years through a common set of immunocompromising conditions and follow-up started the first day of the 2023 vaccination campaign until 12 months later. VE was calculated by time since vaccination (14-59, 60-119, 120-179, 180-365 days after vaccination) for ICPs by pooling study site level confounder adjusted hazard ratios (aHR) of vaccination, estimated with Cox proportional hazards regression models, using a random effect meta-analysis with VE = 100 × (1-pooled aHR). RESULTS: The XBB.1.5 VE was 52% (95% confidence interval (CI): 41 to 60) and 75% (95%CI: 60 to 84) against hospitalization and death, respectively, 14-59 days after vaccination, and VE decreased with time since vaccination with no remaining protection at 180-365 days after vaccination. CONCLUSION: Adapted XBB.1.5 vaccine provided moderate protection within 120 days after vaccination against severe COVID-19 outcomes among ICPs aged ≥18 years during a period with BA.2.86/JN.1 replacing the XBB.1.5 variant.