BackgroundAn objective of the Severe Heterogeneous Asthma Registry, Patient-centered (SHARP) is to produce real-world evidence on a pan-European scale by linking non-standardized, patient-level registry-data. Mepolizumab has shown clinical efficacy in RCTs and prospective real-world studies and could therefore serve as a proof of principle for this novel approach.AimTo harmonize data from 10 national severe asthma registries and characterize patients receiving mepolizumab, assess its effectiveness on annual exacerbations and maintenance oral glucocorticoid (OCS) use, and evaluate treatment patterns.MethodsIn this observational cohort study, registry data (5871 patients) were extracted for harmonization. Where harmonization was possible, patients who initiated mepolizumab between 1-1-2016 and 31-12-2021 were examined. Changes of a 12 (range 11–18) months period in frequent (≥2) exacerbations, maintenance OCS use and dose were analyzed in a privacy-preserving manner using meta-analysis of generalized estimating equation parameters. Periods before and during the COVID-19 pandemic were analyzed separately.ResultsIn 912 patients who fulfilled selection criteria mepolizumab significantly reduced frequent exacerbations (OR;95%CI: 0.18;0.13–0.25), maintenance OCS use (OR;95%CI: 0.75;0.61–0.92) and dose (mean; 95%CI: −3.93 mg·day−1; −5.24–2.62) in the Pre-Pandemic group, with similar trends in the Pandemic group. Marked heterogeneity was observed between registries in patient characteristics and mepolizumab treatment patterns.ConclusionsBy harmonizing patient-level registry data and applying federated analysis, SHARP demonstrated the real-wold effectiveness of mepolizumab on asthma exacerbations and maintenance OCS use in severe asthma patients across Europe, consistent with previous evidence. This paves the way for future pan-European real-world severe asthma studies using patient-level data in a privacy-proof manner.