Inclusion Criteria:  * The availability of the complete data  Duration of treatment with mepolizumab: ≥ 52 weeks Satisfying the Polish drug programme inclusion criteria: Age >18  Before treatment with mepolizumab (BSAT inclusion criteria):  High doses of ICS + one other controlling medication (i.e. LABA) ≥2 exacerbations in the previous year ≥350 eosinophil cells/μl in the blood at the time of qualifying, or in the previous year Pre-bronchodilator FEV1 < 80%  Exclusion Criteria:  * Duration of treatment with mepolizumab < 52 weeks  • Lack of complete data