This study is aimed at evaluation of the efficacy of mepolizumab 100 mg subcutaneously (SC) every 4 weeks in patients with severe eosinophilic asthma who have been treated for at least 12 months in several Polish allergy/asthma centres under the same protocol. Target population to be recruited has been set at 130 subjects from at least 6 asthma centers throughout the country. Data on demographics and asthma status will be collected using questionnaires at 3 time-points: pre-mepolizumab (pre-MEPO), after 24 weeks of mepolizumab (MEPO) and after 1 year of MEPO administration (some of the outcomes will be observed every 4 weeks). Primary endpoints will include:

• Asthma exacerbations measured at qualification for the treatment (in the period of previous 52 weeks) and at the 24th and 52nd week of the treatment.
• Oral Corticosteroids use dose (documented at qualification for the treatment and at the 24th and 52nd week of the treatment).

This study is aimed at evaluation of the efficacy of mepolizumab 100 mg SC every 4 weeks in patients with severe eosinophilic asthma who have been treated for at least 12 months in several Polish allergy/asthma centres under the same protocol. Retrospective multicentre observational study will involve 130 patients with severe eosinophilic asthma (SEA) who have been treated in six Severe Asthma Treatment Centres (SATCs) in Poland. In each SATC all data available in the program questionnaires will be transferred to the Study Data Sheet (questionnaire), and will be send to the study coordinator within 5 months from the study beginning The start-up meeting including partners from all centres involved will be organized to discuss the study protocol and to unify data collection The evaluation parameters (exacerbations rate, OCS dose) will be analysed at least at three time points: pre-MEPO, after 24 weeks of MEPO and after 1 year of MEPO administration (some of the outcomes will be observed every 4 weeks, for the details see 'study endpoints' section).

In addition the following parameters which are available in patients' records will be analysed:

• 5-item asthma control questionnaire (ACQ-5) score (measured at qualification for the treatment and every 4 weeks thereafter)
• Asthma quality of life questionnaire (AQLQ) score (measured at qualification for the treatment and every 4 weeks thereafter)
• Pre-bronchodilator FEV1 (measured at qualification for the treatment and every 4 weeks thereafter)

Research activities will include:

• collecting raw data from the clinical centres (paper version) and constructing a raw dataset (digital version),
• data cleaning, computation of variables,
• statistical analysis typical for pre-post study design (the statistical analysis will be outsourced to the specialized private institute).

Clinical improvements observed at 24 weeks and at 52 weeks of treatment with Mepolizumab will be referred to the following characteristics of patients at baseline:

• demographics,
• presence of comorbidities including the atopic status,
• concomitant pharmacotherapy,
• clinical status,
• eosinophilia. We will control for mepolizumab use regarding dose, treatment duration and dosing frequency as well as for the safety profile based on the AEs reporting in the medical documentation.

Data Source / Data Collection Patients recruited to the study had been treated with mepolizumab between December 2017 and December 2019.All the data planned to be used in the proposed study were systematically collected in the form of the clinical documentation (paper version) and will be transferred in the study centres into the study.

Data Sheets. Collaborating Researchers (Severe Asthma Centres' Leaders) will provide the data input into the dedicated online questionnaire.

Study Population 130 Patients who were treated with mepolizumab in six severe-asthma clinics in Poland between December 2017 and December 2019 . In the drug program in Poland it was mandatory to conduct the control examinations at the 24th and 52nd week of the treatment . In the proposed study we will use this information to evaluate study endpoints. Only patients who have been treated for at least 52 weeks are included into the study

Variables concerning the primary endpoints

• Asthma exacerbations measured at qualification for the treatment (in the period of previous 52 weeks) and at the 24th and 52nd week of the treatment.
• Oral Corticosteroids use dose (documented at qualification for the treatment and at the 24th and 52nd week of the treatment)

Variables concerning the secondary endpoints:

• ACQ-5 score (measured at qualification for the treatment and every 4 weeks thereafter)
• AQLQ score (measured at qualification for the treatment and every 4 weeks thereafter)
• Pre-bronchodilator forced expiratory volume in 1 second (FEV1) (measured at qualification for the treatment and every 4 weeks thereafter)
• Blood eosinophil counts (measured at qualification for the treatment and at the 24th and 52nd week of the treatment)

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 inhaled corticosteroids (ICS) + one other controlling medication (i.e. LABA)
  • ≥2 exacerbations in the previous year
  • ≥350 eosinophil cells/microliter (µl) in the peripheral blood at the time of qualification or in the previous year
  • Pre-bronchodilator FEV1 < 80%

Exclusion Criteria:

* Duration of treatment with mepolizumab < 52 weeks

• Lack of complete data

130 Patients who were treated with mepolizumab in six severe-asthma clinics in Poland between December 2017 and December 2019 . In the drug program in Poland it was mandatory to conduct the control examinations at the 24th and 52nd week of treatment. In the proposed study we will use this information to evaluate study endpoints. Only patients who have been treated for at least 52 weeks are included into the study.

Individual entries regarding laboratory results, concomitant medications, comorbidities and clinical features of asthma exacerbations will be made available upon request, as specified below.

The data may be received upon reasonable written request form the principal investigator.

Throughout the treatment period (weeks 0 through 52)

Two (1.9%) patients were reported to experience adverse events during treatment. One (0.9%) patient experienced a miscarriage after 7th dose of mepolizumab administration. One (0.9%) patient complained of pain in the small joints of the both hands

Retrospective study, basing on reports from national health data system (as per requirements of national health insurance fund). Incompleteness of data for 24 patients, not possible to be retrieved.