An Efficacy and Safety Study of Intravenous Anifrolumab to Treat Systemic Lupus Erythematosus in Pediatric Participants

Inclusion Criteria: * Participant's parent/caregiver/legally authorized representative and participant (if required per local country regulation) capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in this protocol. Informed assent is to be provided by the participant per local country regulation. * Diagnosis of SLE according to the 2019 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) criteria for at least 3 months prior to signing the ICF. * At Screening, participant must have moderate to severe active SLE disease, as adjudicated by the Central Adjudication Committee, defined as: (a) SLEDAI-2K activity of: (i) ≥ 6 points with at least 4 points (≥ 4 points) coming from the following clinical components ('Clinical' SLEDAI-2K score): arthritis, myositis, rash, alopecia, mucosal ulcers, pleurisy, pericarditis, or vasculitis and excluding points attributed to a fever, SLE headache, and organic brain syndrome (ii) Clinical SLEDAI score of ≥ 4 points verified at Day 1 (b) BILAG-2004 activity of: (i) ≥ 1 BILAG A score; or (ii) ≥ 2 BILAG B scores (c) PGA score ≥ 1.0 on a 0 to 3 VAS * Participant should meet all of following tuberculosis (TB) criteria: A. No signs or symptoms of active TB B. No medical history or past physical examinations suggestive of active TB C. No recent contact with a person with active TB or if there has been such contact, referral to a TB specialist for evaluation and initiation of treatment for latent TB, if warranted, prior to the first administration of study intervention in accordance with local SoC D. No history of latent TB without documented completion of treatment prior to initial screening visit * Female participants of childbearing potential must have a negative serum pregnancy test at screening and negative urine pregnancy test at randomization. * Female participants of childbearing and male participants must adhere to the contraception methods. Exclusion Criteria: * Known diagnosis of an IFN-mediated autoinflammatory interferonopathy. * History of, or current diagnosis of, clinically significant non-SLE-related vasculitides. * In participants aged 11 years and above: history or evidence of suicidal ideation. * History of any non-SLE disease that has required treatment with oral or parenteral corticosteroids for more than a total of 2 weeks within the last 24 weeks prior to signing the ICF. * Any positive result on screening for human immunodeficiency virus. * Active hepatitis B surface antigen OR hepatitis B core antibody (HBcAb), hepatitis C virus (HCV) antibody and detectable HCV ribonucleic acid (RNA) or any active or recent case of Herpes Zoster infection. * Any clinical cytomegalovirus or Epstein-Barr virus infection that has not completely resolved within 12 weeks prior to signing the ICF. * History of severe COVID-19 infection requiring hospitalization, intensive care unit care, or assisted ventilation or any prior COVID-19 infection with unresolved sequelae. Any mild/asymptomatic COVID-19 infection (laboratory confirmed or suspected based on clinical symptoms). * Prior use of anifrolumab. * Prior treatment with directly acting cytotoxic B-cell depleting therapeutics (eg, rituximab) \< 26 weeks prior to ICF signature. * Blood transfusion or receipt of blood products except albumin within 4 weeks prior to signing the ICF.