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 aspermitted by local regulatory authorities and ethic committees (ECs)

2. Documented endoscopic biopsy supporting a pathologic diagnosis of Eosinophilicgastritis (EoG) at least 3 months prior to screening

3. Screening endoscopic biopsies with a demonstration of eosinophilic infiltration fora 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 weeksprior 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 perweek for the 2 weeks prior to baseline. An average severity score of ≥4 (on a scaleof 0-10) per week for the 2 weeks prior to baseline for at least 2 of the 6symptoms, 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 withdupilumab

3. Helicobacter pylori infection

4. Any esophageal stricture unable to be passed with a standard, diagnostic, upperendoscope 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 followingconditions: eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)or hyper-eosinophilic syndrome

7. History of bleeding disorders, esophageal or gastric varices that, in the opinion ofthe investigator, would put the participant at undue risk for significantcomplications from an endoscopy procedure

8. Initiation or change of a food-elimination diet regimen or re-introduction of apreviously 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 thestudy

9. Planned or anticipated use of any prohibited medications and procedures during thestudy

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