Study: NCT02836496

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: Mepolizumab 300 mg
Description: Mepolizumab is available as lyophilized powder for injection reconstituted with Sterile Water for Injection, just prior to use.

Intervention type: DRUG
Group type: PLACEBO_COMPARATOR
Intervention: Placebo matching mepolizumab
Description: Placebo is available as 0.9% sodium chloride solution

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: Active OCS capsules (5 mg prednisolone or prednisone)
Description: All subjects will be provided with 2 bottles of blinded OCS capsules, one containing 5mg OCS capsules (active OCS treatment) and a second one containing matching placebo capsules (placebo OCS treatment). These will be dispensed to each subject at each scheduled clinic visit and as needed. Subjects with an increase in blood eosinophils above the pre-specified threshold will be instructed to start blinded OCS treatment from one of the bottles provided (active treatment) unless the subject's HES therapy has already been increased due to a symptom flare within the past 2 weeks.

Intervention type: DRUG
Group type: PLACEBO_COMPARATOR
Intervention: Active OCS capsules (5 mg prednisolone or prednisone)
Description: All subjects will be provided with 2 bottles of blinded OCS capsules, one containing 5mg OCS capsules (active OCS treatment) and a second one containing matching placebo capsules (placebo OCS treatment). These will be dispensed to each subject at each scheduled clinic visit and as needed. Subjects with an increase in blood eosinophils above the pre-specified threshold will be instructed to start blinded OCS treatment from one of the bottles provided (active treatment) unless the subject's HES therapy has already been increased due to a symptom flare within the past 2 weeks.

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: Placebo matching OCS capsules
Description: All subjects will be provided with 2 bottles of blinded OCS capsules, one containing 5mg OCS capsules (active OCS treatment) and a second one containing matching placebo capsules (placebo OCS treatment). These will be dispensed to each subject at each scheduled clinic visit and as needed.A subject who does not reach the pre-specified blood eosinophil threshold with a similar blood draw date will be selected to initiate a placebo OCS treatment in a blinded manner, unless the subject's HES therapy has already been increased due to a symptom flare within the past 2 weeks.

Intervention type: DRUG
Group type: PLACEBO_COMPARATOR
Intervention: Placebo matching OCS capsules
Description: All subjects will be provided with 2 bottles of blinded OCS capsules, one containing 5mg OCS capsules (active OCS treatment) and a second one containing matching placebo capsules (placebo OCS treatment). These will be dispensed to each subject at each scheduled clinic visit and as needed.A subject who does not reach the pre-specified blood eosinophil threshold with a similar blood draw date will be selected to initiate a placebo OCS treatment in a blinded manner, unless the subject's HES therapy has already been increased due to a symptom flare within the past 2 weeks.