This study is researching an experimental drug called dupilumab (called "study drug"). The study is focused on children with active eosinophilic esophagitis (EoE; an inflammatory disease of the esophagus) which impacts feeding and nourishment.

The aim of the study is to see how safe, tolerable, and effective the study drug is when given for 24 weeks to children with active EoE.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drug
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)

Key Inclusion Criteria:

1. Pediatric patients aged ≥6 months and weighing ≥5 kg and <15 kg at screening with active EoE
2. History of symptom(s) determined by the investigator to be the result of EoE in the month prior to screening, as defined in the protocol
3. Baseline endoscopic biopsies, performed during the screening period, with a demonstration on central reading of intraepithelial eosinophilic infiltration in at least 2 of the 3 biopsied esophageal regions, as defined in the protocol

Key Exclusion Criteria:

1. Prior participation in a dupilumab clinical trial or past or current treatment with dupilumab
2. Initiation or change of a food-elimination diet regimen or re-introduction of a previously eliminated food group in the 6 weeks prior to screening. Patients on a food-elimination diet must remain on the same diet throughout the study
3. Other causes of esophageal eosinophilia or the following conditions: eosinophilic gastroenteritis, hypereosinophilic syndrome, and eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)
4. Active Helicobacter pylori infection
5. History of Crohn's disease, ulcerative colitis, celiac disease, or prior esophageal surgery
6. Any esophageal stricture unable to be passed with a standard, diagnostic, upper endoscope or any critical esophageal stricture that requires dilation at screening
7. History of bleeding disorders or esophageal varices that, in the opinion of the investigator, would put the patient at undue risk for significant complications from an endoscopic procedure
8. Treatment with swallowed topical corticosteroids within 8 weeks prior to baseline standard of care endoscopy

NOTE: Other Protocol-Defined Inclusion/Exclusion Criteria Apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf