Comparison of Alemtuzumab and Rebif® Efficacy in Multiple Sclerosis, Study One

Inclusion Criteria: * Given written/signed informed consent * Age 18 to 50 years old (inclusive) as of the date the informed consent form (ICF) was signed * Diagnosis of MS per updated McDonald criteria, and cranial magnetic resonance imaging (MRI) scan demonstrating white matter lesions attributable to MS within 5 years of screening * Onset of MS symptoms (as determined by a neurologist, either at screening or retrospectively) within 5 years of the date the ICF was signed * Expanded Disability Status Scale (EDSS) score 0.0 to 3.0 (inclusive) at screening * Greater than or equal to (\>=) 2 MS attacks (first episode or relapse) occurring in the 24 months prior to the date the ICF was signed, with \>=1 attack in the 12 months prior to the date the ICF was signed, with objective neurological signs confirmed by a physician, nurse practitioner, or other Genzyme-approved health-care provider and the objective signs could be identified retrospectively Exclusion Criteria: * Received prior therapy for MS other than corticosteroids, for example, alemtuzumab, interferons, intravenous immunoglobulin, glatiramer acetate, natalizumab, and mitoxantrone * Exposure to azathioprine, cladribine, cyclophosphamide, cyclosporine A, methotrexate, or any other immunosuppressive agent other than systemic corticosteroid treatment * Any progressive form of MS * History of malignancy (except basal skin cell carcinoma) * CD4 + , CD8 + count, B cell, or absolute neutrophil count less than (\<) lower limit of normal (LLN) at screening * Known bleeding disorder (for example, dysfibrinogenemia, factor IX deficiency, hemophilia, Von Willebrand's disease, disseminated intravascular coagulation, fibrinogen deficiency, or clotting factor deficiency) * Significant autoimmune disease including but not limited to immune cytopenias, rheumatoid arthritis, systemic lupus erythematosus, other connective tissue disorders, vasculitis, inflammatory bowel disease, severe psoriasis * Presence of anti-thyroid stimulating hormone (TSH) receptor (TSHR) antibodies (that is, above the LLN) * Active infection or at high risk for infection