Inclusion Criteria

1. Diagnosis of AD according to the American Academy of Dermatology consensus criteria at the screening visit
2. Patients with documented recent history (within 6 months before the screening visit) of inadequate response to topical AD medication(s)
3. IGA = 4 at screening and baseline visits
4. EASI ≥21 at screening and baseline visits
5. Body Surface Area (BSA) ≥15% at screening and baseline visits

Exclusion Criteria

1. Participation in a prior dupilumab clinical study
2. History of important side effects of medium potency topical corticosteroids (only applicable for part B of the study)
3. Having used immunosuppressive/immunomodulating drugs within 4 weeks before the baseline visit
4. Treatment with a live (attenuated) vaccine within 4 weeks before the baseline visit
5. Active chronic or acute infection requiring treatment with systemic antibiotics, antivirals, antiprotozoals, or antifungals within 2 weeks before the baseline visit.
6. Known history of human immunodeficiency virus (HIV) infection or HIV seropositivity at the screening visit
7. History of malignancy at any time before the baseline visit
8. Diagnosed active endoparasitic infections or at high risk of these infections
9. Severe concomitant illness(es) that, in the investigator's judgment, would adversely affect the patient's participation in the study