Inclusion criteria:  Moderate to severe AtD (confirmed by a dermatologist) according to the Hannifin and Rajka criteria or Eichenfield revised criteria. Onset of AtD symptoms occurring at least 6 months prior to Screening, with stable disease for at least 1 month prior to Screening. Eczema Activity Severity Index greater than or equal to (>=)16; Investigator Global Assessment score >=3. Group 1- Biologic Naïve: Topical First Line Treatment: Documented recent history (within 6 months before Screening) of: a) either an inadequate response (IR) to out-patient treatment with at least one topical treatment (intermittent topical corticosteroid, topical calcineurin inhibitor), topical inhibitors or Phosphodiesterase 4 inhibitor (Crisaborole); b) or that topical treatments were otherwise not recommended. Group 2- Dupilumab-Inadequate Responder: Documented history of an IR to dupilumab: a) either following at least 16 weeks of treatment according to the Investigator's judgement; b) or intolerant to dupilumab owing to adverse events.  Exclusion Criteria:  Other than AtD, the presence of a significant skin morbidity that will influence the Investigator's ability to assess the severity of the disease (e.g. psoriasis, confirmed or suspected cutaneous T-cell lymphoma, autoimmune bullous disease, fixed drug reaction and Stevens Johnson Syndrome). Participants with any uncontrolled medical conditions, other than AtD, that in the opinion of the investigator puts the participant at unacceptable risk or will likely interfere with study assessments or data integrity. Other medical conditions should be stable at the time of screening and be expected to remain stable for the duration of the study. Treatment with biologic agents (investigational and marketed monoclonal antibodies) within 12 weeks or 5 pharmacokinetic half-lives (whichever is longer) prior dosing on Day 1. Treatment with Janus Activated Kinase inhibitors (e.g. baricitinib, upadacitinib) within 4 weeks or 5 half-lives (whichever is longer) prior to dosing on Day 1. Mycophenolate mofetil, azathioprine, methotrexate, or calcineurin inhibitors within 4 weeks of Screening.