This study aims to check the long-term safety of a drug called ianalumab for people with systemic lupus erythematosus (SLE). SLE is a disease where the immune system attacks healthy tissues by mistake. This study is for people who finished a previous part of the research called SIRIUS-SLE. In this extension study, participants will continue taking ianalumab either once a month or less often, or a placebo (a fake treatment), to see how well they handle it over time.

• Participants must have completed a previous study phase.
• They must not be on certain restricted treatments and should not have any major infections or plan to get live vaccines.
• Pregnant or nursing women can't join, and participants should use effective birth control if they're able to have children.

Before joining, participants need to sign a consent form (or have a parent/legal guardian do so if under 18). This study is important to ensure that ianalumab can be safely used for treating SLE over a long period.