A Study to Assess the Safety and Efficacy of Elezanumab When Added to Standard of Care in Relapsing Forms of Multiple Sclerosis

Inclusion Criteria: * Participant has diagnosis of relapsing remitting multiple sclerosis (RRMS) or secondary-progressive multiple sclerosis (SPMS) with relapses within the past 24 months. * Participant has cranial magnetic resonance imaging (MRI) demonstrating lesion(s) consistent with multiple sclerosis (MS). * Participant has evidence of physical disability according to Expanded Disability Status Scale (EDSS) or Timed 25-Foot Walk (T25FW) or 9-Hole Peg Test. Exclusion Criteria: \- Participants must not have experienced or be recovering from a clinical MS relapse within 6 months of Screening.