This clinical trial is focused on studying a condition known as Eosinophilic Granulomatosis with Polyangiitis (EGPA), which was previously called Churg-Strauss syndrome. EGPA is a rare disease that causes inflammation of blood vessels, leading to damage in various organs. The study aims to evaluate the effectiveness of a treatment regimen based on Mepolizumab, a medication that helps reduce inflammation by targeting specific cells in the immune system. This regimen will be compared to a conventional treatment strategy to see if it can help patients achieve remission, which means a reduction or disappearance of disease symptoms.

Participants in the study will receive either the Mepolizumab-based treatment or a conventional treatment, which may include medications like Cyclophosphamide and Azathioprine. Cyclophosphamide is a medication used to suppress the immune system, while Azathioprine is often used to prevent the body from rejecting transplanted organs and to treat autoimmune diseases. Some participants may also receive a placebo, which is a substance with no active medication, to help compare the effects of the treatments. The study will monitor the participants over a period to assess the impact of these treatments on their condition.

The main goal of the study is to determine if the Mepolizumab-based regimen can reduce the need for glucocorticoids, a type of steroid medication, in patients with newly diagnosed or relapsing EGPA. The study will track the dosage of a specific glucocorticoid called prednisone, aiming for a dose of 4.0 mg or less per day by a certain point in the study. Participants will be closely monitored for any changes in their condition, including any relapses or flare-ups of symptoms, as well as any side effects from the treatments. The study will provide valuable information on the potential benefits of Mepolizumab for managing EGPA.