Efficacy and Safety of Benralizumab in Patients With Eosinophilic Gastritis and/or Gastroenteritis (The HUDSON GI Study)

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.