A Study to Evaluate How Safe Pozelimab + Cemdisiran Combination Therapy is and How Well it Works in Adult Patients With Paroxysmal Nocturnal Hemoglobinuria (PNH) Who Have Not Recently Received or Have Not Received Complement Inhibitor Treatment

Key Inclusion Criteria:

Diagnosis of PNH confirmed by high-sensitivity flow cytometry testing with PNH granulocytes or monocytes as described in the protocol
Active disease, as defined by the presence of 1 or more PNH-related signs or symptoms as described in the protocol
LDH level ≥2 × ULN at the screening visit
Willing and able to comply with clinic/remote visits and study-related procedures, including completion of the full series of meningococcal vaccinations required per protocol

Key Exclusion Criteria:

Prior treatment with eculizumab within 3 months prior to screening, ravulizumab within 6 months prior to screening, or other complement inhibitors within 5 half-lives of the respective agent prior to screening
Receipt of an organ transplant, history of bone marrow transplantation or other hematologic transplant
Body weight <40 kilograms at screening visit
Planned use of any complement inhibitor therapy other than study drugs during the treatment period
Not meeting meningococcal vaccination requirements and, at a minimum documentation of quadrivalent meningococcal vaccination within 5 years prior to the screening visit and serotype B vaccine (when available) within 3 years prior to the screening visit as described in the protocol.
Any contraindication for receiving Neisseria meningitidis vaccinations (serotypes ACWY and B).
Unable to take antibiotics for meningococcal prophylaxis (if required by local ravulizumab [Cohort A] or eculizumab [Cohort B] prescribing information, where available, or national guidelines/local practice, or if necessary when administration of the first dose of the vaccination is less than 2 weeks prior to study treatment initiation)
Any active, ongoing infection or a recent infection requiring ongoing systemic treatment with antibiotics, antivirals, or antifungals within 2 weeks of screening or during the screening period
Documented history of active, uncontrolled, ongoing systemic autoimmune diseases

Note: Other protocol-defined Inclusion/ Exclusion Criteria apply