A Study to Evaluate Efficacy, Safety, and Tolerability of Alemtuzumab in Pediatric Patients With RRMS With Disease Activity on Prior DMT

Inclusion criteria : * Participants with RRMS aged from 10 years to \<18 years at study entry are eligible. Participants must meet the criteria of diagnosis of MS as defined by the International Pediatric MS Study Group (IPMSSG) criteria for pediatric MS and the criteria of MS based on 2010 McDonald criteria. * Signed written informed consent/assent obtained from participant and participant's legal representative (parent or guardian) according to local regulations. * Expanded Disability Status Scale (EDSS) score of 0.0 to 5.0 (inclusive) at screening. * At least 2 recorded MS attacks and at least 1 MS attack (relapse) in the last year during treatment with a beta interferon therapy (IFNB) or glatiramer acetate (GA) after being on that therapy for at least 6 months, and was currently still taking the same therapy. * At least 1 of the following: * \>=1 new or enlarging T2 hyperintense lesion or gadolinium enhancing lesion while on that same prior therapy (IFNB or GA), or * Two or more relapses in the prior year, or * Tried at least 2 MS DMTs. Exclusion criteria: * Any progressive or non-relapsing forms of MS. * Conditions/situations such as: * Impossibility to meet specific protocol requirements. * Current participation in another interventional clinical study. Participants who are treated with a comparator agent approved for screening inclusion (INF or GA) may be considered for this trial. * Participant is the Investigator or any Sub-Investigator, research assistant, pharma…