This study is designed to evaluate the efficacy, safety and pharmacokinetics of crovalimab compared with placebo as adjunct therapy in the prevention of VOEs in participants with SCD.

Inclusion Criteria:

• Body weight >=40 kg.
• Male or female with confirmed diagnosis of HbSS (SCD genotype of sickle cell anemia) or HbSβ0 (SCD genotype of sickle cell beta zero thalassemia).
• Two or more (>=2) to <=10 documented VOEs in the 12 months prior to randomisation.
• If receiving concurrent SCD-directed therapy, the participant must have been on a stable dose for a minimum of 3 months prior to study enrollment. There should be no plans to modify the participants' dosing throughout the study duration, other than for safety reasons.
• If receiving erythropoietin, the participant must have been prescribed this medication for the preceding 3 months and be dose-stabilised for at least 3 months prior to study enrollment.
• Vaccination against N. meningitides serotypes A, C, W, and Y and Vaccinations against H. influenza type B and S. pneumonia.
• Participants who have been vaccinated (partially or in full) against SARS-CoV-2 with a locally approved vaccine are eligible to be enrolled in the study, 3 days or longer after inoculation.
• Adequate hepatic and renal function.
• For women of childbearing potential: agreement to remain abstinent or use contraception during the treatment period and for 10.5 months after the final dose of study treatment.

Exclusion Criteria:

• History of hematopoietic stem cell transplant.
• Participating in a chronic transfusion program and/or planning on undergoing an exchange transfusion during the duration of the study.
• History of hypersensitivity, allergic, or anaphylactic reactions to any ingredient contained in the study treatment.
• Received active treatment on another investigational trial within 28 days (or within five half-lives of that agent, whichever is greater) prior to screening visit, or plans to participate in another investigational drug trial.
• Hemoglobin <6 g/dL.
• Known or suspected hereditary complement deficiency.
• Active systemic bacterial, viral, or fungal infection within 14 days before first drug administration.
• Presence of fever (>=38 degrees Celsius) within 7 days before the first drug administration.
• Immunised with a live attenuated vaccine within 1 month before first drug administration.
• Pregnant or breastfeeding, or intending to become pregnant during the study or within 10.5 months after the final dose of study treatment.
• Known HIV infection with documented CD4 count <200 cells/microliter within 24 weeks prior to screening.
• History of N. meningitidis infection within the prior 6 months.

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing.