Study of the Efficacy of Early Intervention With Secukinumab 300 mg s.c. Compared to Narrow-band UVB in Patients With New-onset Moderate to Severe Plaque Psoriasis

Key Inclusion Criteria: * Able to understand and communicate with the investigator, willing and capable to comply with all study procedures, and provide written signed and dated informed consent (personally or by a witness) before any assessment is performed. * Aged 18 to 50 years inclusive. * New-onset plaque psoriasis with appearance of the first psoriasis plaques within the last 12 months before randomization and naïve to any systemic treatment and phototherapy (Arm A1, Arm A2, and Arm B1). Episodes of mild psoriasis, which occurred at least 3 years before screening and resolved spontaneously within 6 months will be accepted. * Chronic plaque psoriasis with appearance of the first psoriasis symptoms 5 years or longer and intolerance or inadequate response to phototherapy or any systemic treatment including biologicals, except for IL-17A inhibitors (Arm C1 and Arm C2). * Moderate to severe plaque psoriasis defined at screening and baseline by PASI \>= 10, and body surface area (BSA) \>= 10%, and IGA mod 2011 \>= 3. Key Exclusion Criteria: * Forms of psoriasis other than plaque-type (e.g., pustular, erythrodermic, guttate, light sensitive, and drug induced). * Ongoing use of prohibited treatments. * Previous treatment with phototherapy or any systemic treatment. * Pregnant or nursing (lactating) women. * Women of childbearing potential, defined as all women physiologically capable of becoming pregnant, unless they are using effective methods of contraception during the Treatment period or longer if required by locally approved prescribing information (e.g., 20 weeks in the EU and countries where applicable for secukinumab).