A Study to Learn How Well Dupilumab Works in Adult and Adolescent Participants With Eosinophilic Gastritis With or Without Eosinophilic Duodenitis and the Side Effects it May Have

Key Inclusion Criteria: 1. Adolescent participants will only be enrolled at study sites in countries/regions as permitted by local regulatory authorities and ethic committees (ECs) 2. Documented endoscopic biopsy supporting a pathologic diagnosis of Eosinophilic gastritis (EoG) at least 3 months prior to screening 3. Screening endoscopic biopsies with a demonstration of eosinophilic infiltration for a diagnosis of EoG, as defined in the protocol 4. Completed at least 11 of 14 days of EoG/EoD-SQ eDiary data entry in the 2 weeks prior to the baseline visit 5. History (by participant report) of at least 2 episodes of EoG (with or without EoD) symptoms per week in 8 weeks before screening, as defined in the protocol 6. An average TSS of ≥ 20 calculated using data collected via the EoG/EoD-SQ eDiary per week for the 2 weeks prior to baseline. An average severity score of ≥4 (on a scale of 0-10) per week for the 2 weeks prior to baseline for at least 2 of the 6 symptoms, as defined in the protocol. Key Exclusion Criteria: 1. Body weight less than 40 kg at screening 2. Prior participation in a dupilumab clinical trial, or past or current treatment with dupilumab 3. Helicobacter pylori infection 4. Any esophageal stricture unable to be passed with a standard, diagnostic, upper endoscope or any critical esophageal stricture that requires dilation at screening 5. History of achalasia, Crohn's disease, eosinophilic colitis, ulcerative colitis, celiac disease, and prior gastric or duodenal surgery, as defined in the protocol 6. Other causes of gastric and, if applicable, duodenal eosinophilia or the following conditions: eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome) or hyper-eosinophilic syndrome 7. History of bleeding disorders, esophageal or gastric varices that, in the opinion of the investigator, would put the participant at undue risk for significant complications from an endoscopy procedure 8. Initiation or change of a food-elimination diet regimen or re-introduction of a previously eliminated food group in the 4 weeks prior to the screening visit. Participants on a food-elimination diet must remain on the same diet throughout the study 9. Planned or anticipated use of any prohibited medications and procedures during the study 10. Planned or anticipated major surgical procedure during the study 11. Receiving tube feeding or parenteral nutritional at screening NOTE: Other Protocol Defined Inclusion / Exclusion Criteria Apply