The primary objective of this study is to confirm the efficacy, safety, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of ravulizumab in the treatment of Chinese adults with anti-aquaporin-4 (AQP4) antibody (Ab) + neuromyelitis optica spectrum disorder (NMOSD).

Key Inclusion (essential)

• Diagnosis: NMOSD per 2015 international consensus criteria, and anti AQP4 antibody positive at Screening.
• Disease activity: ≥1 attack/relapse in the past 12 months.
• Disability: EDSS ≤7.
• Background therapy: If on IST and/or oral corticosteroids, participant should be on a stable maintenance regimen prior to Screening and plan to remain stable during the study unless relapse occurs. (Detailed agent specific duration/dose rules to be confirmed at screening.)
• Body weight: ≥40 kg.
• Vaccinated against meningococcal infections from serogroups A, C, W, Y (and B where available) within the 3 years prior to study intervention administration on Day 1.

Key Exclusion (essential)

• Pregnancy/lactation: Pregnant, breastfeeding, or intending to conceive during the study.

• Infection risk: History of meningococcal disease or unresolved meningococcal disease, active systemic infection within 14 days, or fever ≥38°C within 7 days before Day 1.

• Hypersensitivity: To murine proteins or ravulizumab excipients.

• Serious comorbidities: Any condition that in the Investigator's judgment adds risk or interferes with participation/assessment.

• Viral infections: Known HIV, active HBV, or active HCV.

• Prior/concomitant immunomodulatory treatments:

  • B cell-depleting therapy (e.g., rituximab, inebilizumab) within 3 months before Screening.
  • Mitoxantrone or satralizumab within 3 months before Screening.
  • IVIg within 3 weeks before Screening.
  • Any prior or current complement inhibitor.

Note: Other protocol-defined criteria may apply and should be verified during full eligibility review.

Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.