A Study Utilising Data From European Union (EU) National Multiple Sclerosis (MS) Registries to Assess the Incidence of Anti-Natalizumab Antibody Among Participants Who Receive Subcutaneous Administration of Natalizumab for Treatment of Relapsing-remitting Multiple Sclerosis (RRMS)

The primary objective of this study is to estimate the incidence of Anti-Natalizumab Antibodies (ANAs) in the cohort of natalizumab-naïve and other MS monoclonal antibody (mAb)-naive participants who start receiving natalizumab subcutaneous (SC) injections. The secondary objectives of this study are to estimate the proportion of participants detected with ANAs when switched from natalizumab intravenous (IV) to natalizumab SC (natalizumab-experienced cohort); to evaluate serious adverse events (SAEs), including injection reactions and hypersensitivity reactions, by ANA status and to assess the proportion of participants who had MS relapse, by ANA status.

Key Inclusion Criteria: * Participants who are natalizumab-naïve and other MS mAb-naive and who start on natalizumab SC. * Participants who have previously received natalizumab IV and switch from natalizumab IV to SC administration. Key Exclusion Criteria : * For the natalizumab-naive and other MS mAb-naive cohort, participants who previously received natalizumab or other MS mAbs will be excluded. * For the natalizumab-experienced cohort, participants who are naive to natalizumab will be excluded. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.