A Study to Evaluate the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Crovalimab in Participants With Guillain-Barré Syndrome (GBS)

Inclusion Criteria: * Body weight \>= 40 kg at screening * Confirmed diagnosis of GBS according to National Institute of Neurological Disorders and Stroke (NINDS) classification system * Onset of weakness due to GBS within 2 weeks before randomization * Able to start the first dose of blinded study drug within 2 weeks of onset of weakness * Able to climb a flight of stairs prior to GBS * Unable to walk independently for \>=10 meters (FG \>=3) with deteriorating weakness as per investigator judgment, or FG 4 or FG 5 on the GBS-DS. These criteria must be satisfied during screening. * Undergoing or starting IVIg treatment (400 mg/kg QD for 5 days) prior to first blinded study drug administration. Participants must be able to receive the first dose of blinded study drug before the final dose of IVIg during the 5-day period of IVIg treatment. * A record of vaccination (\<=3 years) against Neisseria meningitidis, Haemophilus influenzae type B, and Streptococcus pneumonia prior to initiation of blinded study drug, in accordance with most current local guidelines as applicable for patients with complement deficiency. * Adequate hepatic and renal function * For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraception during the treatment period and for up to 11 months after the final dose of study treatment. Exclusion Criteria: * Clear clinical and historical evidence of significant or disabling acute …