Determine Effectiveness of Anifrolumab In SYstemic Sclerosis (DAISY)

This is a multicenter, randomized, double-blind, placebo-controlled, Phase III study to evaluate the efficacy and safety of anifrolumab in the treatment of adult participants with Systemic Sclerosis (SSc) who may be taking one or a combination of protocol-specified standard therapies. The use of one of the following standard immunosuppressant therapies is permitted at a stable dose, but not mandated: hydroxychloroquine, mycophenolate mofetil (MMF), mycophenolic acid or mycophenolate sodium (MPA/MPS), methotrexate, azathioprine, tacrolimus, and oral glucocorticoids. MMF or MPA/MPS, azathioprine, and methotrexate may be used in combination with hydroxychloroquine and/or low-dose oral glucocorticoids \[≤ 10 mg/day\]. Approximately 306 eligible participants will be randomized in a 1:1 ratio to receive either anifrolumab (or matching placebo) given subcutaneously once weekly for 52 weeks. The study will be stratified by the following factors: * Interstitial lung disease (ILD) (yes, no) at Week 0 (Day1); * MMF or MPA/MPS use (yes ,no) at Week 0 (Day 1); and * Disease duration, defined as the time from the first non-Raynaud's symptom attributable to SSc (\<18 months, ≥ 18 months) at Week 0 (Day 1) Study treatment will be administered subcutaneously via an accessorized prefilled syringe by study staff or by the participant or carer, either in the clinic or at home, with most doses being administered at home. The study consists of 4 periods: a 6-week screening period, a 52-week, double-blind, placebo-controlled period, a 52-week open-label active treatment period, and a 12-week safety follow-up period. There are a total of 16 study visits with most visits in the treatment period occurring every 8 to 12 weeks. The periods are described below: * Screening Period: This may involve one or more visits to the study site. * Double Blind Treatment Period: Treatment Period when participants will receive once weekly injections of anifrolumab or matching placebo. Participation will involve in-clinic study visits at Weeks 0 (Day 1), 1, 4, 8\*, 16, 24, 36, 48 and 52. \*The visit at Week 8 may be either by telephone or in person. * Open Label Treatment Period: At Week 52, all participants will be given anifrolumab (subcutaneous) once weekly for 52 weeks (last dose at Week 103). Participation will involve in-clinic study visits at Weeks 52, 53\*, 56, 64, 76. 88 and 104. \*The visit at Week 53 may be either by telephone or in person. * Safety Follow-up Period: All participants will return to the clinic for a 12-week post treatment visit. This will occur post Double Blind Treatment Period (Week 52 or Double Blind Period early discontinuation) or post Open Label Treatment Period (Week 104 or Open Label Period early discontinuation).