Depemokimab in Participants With Hypereosinophilic Syndrome, Efficacy, and Safety Trial

Inclusion Criteria:

* Participants who are greater than or equal (\>=) 40 kilogram (kg) at Screening Visit 1.
* Participants who have a documented diagnosis of HES prior to Visit 2.
* A history of 2 or more HES flares within the past 12 months prior to Visit 1.
* A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: a) woman of non-childbearing potential (WONCBP) Or b) woman of childbearing potential (WOCBP) and using a contraceptive method that is highly effective, with a failure rate of less than (\<) 1 percentage (%).
* Capable of giving signed informed consent.

Exclusion Criteria:

* Participants with HES disease manifestations which in the opinion of the investigator may put the participant at unacceptable risk from study participation or confound interpretation of efficacy or safety data.
* Participants with chronic or ongoing active infections requiring systemic treatment or a pre-existing parasitic infestation within 6 months prior to Visit 1.
* Participants with a known immunodeficiency (e.g., Human Immunodeficiency Virus \[HIV\]), other than that explained by the use of OCS or other therapy taken for HES.
* Participants with a history of or current lymphoma.
* Participants with current malignancy or previous history of cancer in remission for less than 5 years prior to Visit 1. Participants that had localized carcinoma (i.e., basal or squamous cell) of the skin which was resected for cure will not be excluded.
* Participants with a haematologic malignancy with hypereosinophilia in which HES is not the primary diagnosis, e.g., chronic myeloid leukaemia, myelodysplastic syndrome, chronic eosinophilic leukaemia-not otherwise specified.
* Cirrhosis or current unstable liver or biliary disease per investigator assessment.
* Participants who have severe or clinically significant cardiovascular disease uncontrolled with standard treatment.
* Participants with current diagnosis of vasculitis.
* Hypereosinophila with no clinical symptoms and/or proof of organ dysfunction.
* Clinical diagnosis of Eosinophilic granulomatosis with polyangiitis (EGPA).
* Participants with an allergy/ intolerance to a monoclonal antibody or biologic, or any of the excipients of the investigational product.
* Participants who have a previous documented failure with anti-interleukin (IL)-5/5R therapy.
* Participants who have received monoclonal antibodies (mAb) within 30 days or 5 half-lives, whichever is longer, prior to Visit 1.
* Participants who test positive for the FIP1L1-PDGFRα fusion gene.
* QT interval corrected for heart rate according to Fridericia's formula (QTcF) ≥450 milliseconds (msec) or QTcF ≥480 msec for participants with Bundle Branch Block at Screening Visit 1.
* Participants who are not responsive to OCS based on clinical response or blood eosinophil counts in the opinion of the Investigator.
* Participants who are pregnant or breastfeeding.