The main purpose of this trial is to investigate what happens to the trial drug in the body and to confirm that it is safe to use and effective for treating atopic dermatitis (AD) in children.

The trial will last up to maximum of approximately 194 weeks, and there will be up to 59 visits. The visits will be held approximately every second week for the first 68 weeks, then the visits will be held every six weeks for the rest of the treatment period. From week 26, every second visit will be held by phone and every second visit will be held on site.

The first part of the trial is called a screening period and will last between 2 and 6 weeks. After the screening period, the trial drug will be administered to the child by subcutaneous (SC) injection. The treatment period with tralokinumab is divided in 3 parts: 1.) initial treatment period for 16 weeks, 2.) open-label treatment period for 52 weeks and 3.) long-term extension treatment period for up to 106 weeks followed by a 14-week safety follow-up period.

All children will use an emollient twice daily (or more) for at least 14 days prior to start of treatment and will continue this treatment throughout the trial. If medically necessary, rescue treatment for AD is allowed at the discretion of the trial doctor.

Inclusion Criteria:

• Diagnosis of AD (as defined by Hanifin and Rajka criteria for AD).
• Age 6 to <12 years at time of the baseline visit.
• Body weight at baseline of ≥17 kg.
• History of AD for ≥ 12 months at screening.
• History of TCS and/or TCI treatment failure (due to inadequate response or intolerance) or subjects for whom these topical AD treatments are medically inadvisable.
• AD involvement of ≥10% body surface area at screening and baseline.
• An EASI score of ≥16 at screening and at baseline.
• An Investigator's Global Assessment (IGA) score of ≥3 at screening and at baseline.
• Emollient twice daily (or more) for at least 14 days prior to baseline.

Exclusion Criteria:

• Active dermatologic conditions that may confound the diagnosis of AD or would interfere with assessment of treatment.

• Treatment with topical PDE-4 inhibitor within 2 weeks prior to randomization.

• Treatment with the following immunomodulatory medications or bleach baths within 4 weeks prior to baseline:

  • Systemic immunosuppressive/immunomodulating drugs (e.g. methotrexate, cyclosporine, azathioprine, mycophenolate mofetil, JAK inhibitors).
  • Systemic corticosteroid use (excludes topical, inhaled, ophthalmic, or intranasal delivery).
  • 3 or more bleach baths during any week within the 4 weeks.

• Receipt of any marketed biological therapy or investigational biologic agents (including immunoglobulin, anti-IgE, or dupilumab):

  • Any cell-depleting agents, including but not limited to rituximab: within 6 months prior to baseline, or until lymphocyte count returns to normal, whichever is longer.
  • Other biologics (including dupilumab): within 3 months or 5 halflives, whichever is longer, prior to baseline.

• Active chronic or acute infection requiring treatment with systemic antibiotics, antivirals, antifungals, or antiprotozoals within 2 weeks before the baseline visit.

• History of malignancy at any time before the baseline visit.

• History of anaphylaxis following any biological therapy.

• History of immune complex disease.

• Active or suspected endoparasitic infections.

• History of past or current tuberculosis or other mycobacterial infection.

• Established diagnosis of a primary immunodeficiency disorder.

This trial will be assessor blinded (efficacy and safety assessments) to ensure an objective evaluation of efficacy and safety of the Investigational Medicinal Product (IMP). Due to differences in number of injections of IMP, blinding will only be maintained for the assessor. For the initial treatment period (Week 0-Week 16), the assessor will be a different person than the person administering the IMP. Subjects and the caregivers will be instructed that it is important for the trial results that they refrain from revealing their treatment allocation to the assessor.