A Double-masked, Placebo-controlled Study With Open Label Period to Evaluate MEDI-551 in Neuromyelitis Optica and Neuromyelitis Optica Spectrum DisordersTo compare the efficacy of MEDI-551 versus placebo in reducing the risk of an NMO/NMOSD attack in subjects with NMO/NMOSD. Recruiting Principal Investigator Robert CarruthersBody Locations and Systems Neurologic Diseases, Vision Impairment and BlindnessArea VancouverAge 18 and above