Efficacy, Safety, Pharmacokinetics, Pharmacodynamics, and Immunogenicity Study of Ravulizumab in Chinese Adults With Neuromyelitis Optica Spectrum Disorder (NMOSD)

• Ravulizumab (Drug): Participants will receive ravulizumab via intravenous (IV) infusion.

Primary outcomes

• Adjudicated On-Trial Annualized Relapse Rate (ARR) [Baseline up to Week 50]

Secondary outcomes

• Number of Participants With Clinically Important Change From Baseline in Hauser Ambulation Index (HAI) Score [Baseline up to Week 50]
• Number of Participants With Clinically Important Worsening From Baseline in Expanded Disability Status Scale (EDSS) Score [Baseline up to Week 50]
• Change From Baseline in European Quality of Life Health 5-item Questionnaire (EQ-5D) Index Score [Baseline, Week 50]
• Change From Baseline in EQ-5D Visual Analog Scale (VAS) Score [Baseline, Week 50]
• Number of Participants With Treatment Emergent Adverse Events (TEAEs), Treatment Emergent Serious Adverse Events (TESAEs) and Adverse Events of Special Interests (AESIs) [Baseline up to Week 50]
• Serum Ravulizumab Concentration [Day 1 to Day 351]
• Change From Baseline in Serum Free Complement Component 5 (C5) Concentration [Baseline Up to Day 351]
• Number of Participants With Anti-Drug Antibodies (ADAs) [Day 1 up to Day 351]
• Number of Participants With Neutralizing Antibodies (NAb) [Day 1 up to Day 351]

Sex: All, ages: 18 Years to 130 Years

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.