The study was terminated by the Sponsor based on emerging evidence in the pathology of eosinophilic upper gastrointestinal diseases. Recruitment for the study was terminated and only a small number of patients were recruited.

This is a 3-part study. Part A is randomized, double-blinded, placebo-controlled and includes patients with eosinophilic gastritis and/or duodenal-only disease. After completing Part A, participants can continue to Part C - open-label benralizumab treatment period. Following the decision to close enrollment, patients in both Part A and Part C will be given the option to proceed to 6-months of open-label benralizumab treatment in Part D.

Inclusion criteria:

• Aged >= 12 years of age at the time of signing the ICF or informed consent or assent form.
• Confirmed diagnosis of EG/EGE for at least 3 months prior to screening.
• Baseline Eosinophilic gastritis, with or without duodenitis, or eosinophilic duodenitis alone confirmed by biopsy with a gastric count of ≥30 eosinophils/hpf in at least 5 hpfs and/or duodenal eosinophil count ≥30 eosinophils/hpf in at least 3 hpfs without any other cause for the gastrointestinal eosinophilia.
• Symptoms including at least moderate abdominal pain, nausea, bloating, early satiety, and/or loss of appetite
• Must be adherent to daily PRO assessments including at least 8 of 14 symptom assessments in the 14 days prior to randomization
• If on background medications for EG/EGE, the medications should be stable at least 4 weeks prior to the run-in period.
• Willing and able to comply with all study procedures and visit schedule including follow-up visits
• Women of childbearing potential must agree to use a highly effective form of birth control (confirmed by the Investigator) from randomization throughout the study duration and within 12 weeks after last dose if IP.

Exclusion criteria:

• Other gastrointestinal disorders such as active Helicobacter pylori infection, history of achalasia, esophageal varices, Crohn's disease, ulcerative colitis, inflammatory bowel disease, or celiac disease.
• Hypereosinophilic syndrome or eosinophilic granulomatosis with polyangiitis.
• Current malignancy, or history of malignancy, except for patients who have had basal cell, localized squamous cell carcinoma of the skin, or in situ carcinoma of the cervix are eligible provided that the patient is in remission and curative therapy was completed at least 12 months prior to the date of informed consent.
• History of anaphylaxis to any biologic therapy or vaccine.
• Current active liver disease.
• Helminth parasitic infection diagnosed within 24 weeks prior to the date informed that has not been treated with or has failed to respond to standard of care therapy.
• Known immunodeficiency disorder including testing positive for HIV.
• Concomitant use of immunosuppressive medication.
• Receipt of live attenuated vaccines 30 days prior to date of informed consent or assent.
• Receipt of inactive vaccines within 7 days of informed consent or assent.
• Initiation or change of a food-elimination diet regimen or re-introduction of a previously eliminated food group from 6 weeks prior to start of the run-in period and unable or unwilling to remain on a stable diet until the completion of Part A and C.
• Currently pregnant or breast-feeding.

Qualified researchers can request access to anonymised individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal. All requests will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA Pharma Data Sharing Principles. For details of our timelines, please refer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure

When a request has been approved AstraZeneca will provide access to the de- identified individual patient-level data in an approved sponsor tool. Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure

This is a parallel-group efficacy and safety study with 2 arms that are participant and investigator blinded, with an open-label extension.