A Study to Evaluate the Efficacy and Safety of Eculizumab in Guillain-Barré Syndrome

Inclusion Criteria: * Participants who meet the GBS criteria. * Participants who were able to run prior to onset of GBS symptoms. * Participants with onset of weakness due to GBS \< 2 weeks before screening. * Participants unable to walk unaided for ≥ 5 meters (progressively deteriorating FG3 or FG4 to FG5). * Participants who are already on IVIg or deemed eligible for and who will start IVIg. * Participants who can start their first dose of study drug before the end of the IVIg treatment period. Exclusion Criteria: * Participants who have previously received or are currently receiving treatment with complement modulators. * Participants who have been administered another investigational product within 30 days or 5 half-lives (whichever is longer) prior to providing consent or are currently participating in another interventional study. * Participants who have received rituximab within 12 weeks prior to screening. * Participants who are being considered for or are already on plasmapheresis. * Participants who have received immunosuppressive treatment during the 4 weeks prior to providing consent.