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. 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 g/dL. Platelet count >=100,000/µL. Participants receiving sickle cell 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 6 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 >48 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 6 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.