This study looks at how safe and effective a drug called benralizumab is for people with **Hypereosinophilic Syndrome (HES)**. HES is a condition where there are too many eosinophils, a type of white blood cell, which can cause organ damage. The study is "double-blind," meaning neither the doctors nor the patients know who is getting benralizumab or a placebo (a substance with no active medicine), and it lasts for 24 weeks. After this, all participants get the real drug. The medicine is given as an **injection under the skin (SC injection)** every 4 weeks.

• The study lasts 24 weeks, with an additional period where all get the real drug.
• Participants must be 12 years or older and have a stable HES treatment before joining.
• Some people can't join if they have certain health issues like severe heart problems or active infections.

This study requires regular visits and tests to see how the drug works and if it's safe. It's important to discuss with your doctor if joining is right for you.