The purpose of this study is to evaluate crovalimab for the treatment of a sickle cell pain crisis (also known as a VOE) that requires hospitalisation in adult and adolescent participants with SCD. The primary objective of this study is safety and will additionally evaluate pharmacokinetics (how crovalimab is processed by your body), pharmacodynamics (how your body reacts to crovalimab) and the preliminary efficacy of crovalimab compared with placebo.

Inclusion Criteria:

• Body weight >=40 kg.
• Confirmed diagnosis of HbSS (SCD genotype of sickle cell anemia) or HbSβ0 (SCD genotype of sickle cell beta zero thalassemia).
• Vaccination against Neisseria Meningitidis serotypes A, C, W, and Y.
• Vaccinations against H. influenzae type B and S. pneumoniae.
• Participants vaccinated against SARS-CoV-2 are eligible, as long as it has been 3 days or more after inoculation with the vaccine.
• Diagnosis of an acute uncomplicated VOE, that requires admission to a hospital/acute medical facility and treatment with parenteral opioid analgesics.
• Adequate hepatic and renal function.
• Hemoglobin >=5 grams/deciliter (g/dL)
• Platelet count >=100,000/microliter (µL)
• Participants receiving SCD-directed therapies must be on a stable dose for >=28 days.
• For female participants of childbearing potential, an agreement to remain abstinent or use contraception for 322 days (approximately 10.5 months) after the dose of study treatment.

Exclusion Criteria:

• More than 10 VOEs within the last 12 months prior to presentation, that have required a medical facility visit.
• Pain related to the current VOE ongoing for >36 hours.
• Acute pain related to avascular necrosis, hepatic or splenic sequestration, or priapism.
• Pain atypical of an acute uncomplicated VOE.
• Evidence of or suspicion of ACS.
• Evidence or high suspicion of a severe systemic infection.
• Major surgery and/or hospitalization for any reason within 30 days.
• History of Neisseria meningitidis infection within 6 months prior.
• Known HIV infection with a documented CD4 count <200 cells/µL.
• Transfusion or receipt of blood products within 3 months or current participation in a chronic transfusion protocol.
• Immunized with a live attenuated vaccine within 30 days.
• History of hematopoietic stem cell transplant.
• Known or suspected hereditary complement deficiency.
• Pregnant or breastfeeding, or intending to become pregnant during the study or within 322 days (approximately 10.5 months) after the study drug administration.
• Participation in another interventional treatment study with an investigational agent or use of any experimental therapy within the prior 28 days or within five half-lives of that investigational product, whichever was greater.

Qualified researchers may request access to individual patient level data through the clinical study data request platform (www.vivli.org). Further details on Roche's criteria for eligible studies are available here (https://vivli.org/ourmember/roche/). For further details on Roche's Global Policy on the Sharing of Clinical Information and how to request access to related clinical study documents, see here (https://www.roche.com/research\_and\_development/who\_we\_are\_how\_we\_work/clinical\_trials/our\_commitment\_to\_data\_sharing.htm).