A Study to Evaluate How Pozelimab + Cemdisiran Combination Therapy Works in Adult Patients With Paroxysmal Nocturnal Hemoglobinuria (PNH) Whose Current Treatment is Not Working Efficiently

Key Inclusion Criteria: 1. Diagnosis of PNH confirmed by a history of high-sensitivity flow cytometry from prior testing 2. Currently treated with marketed eculizumab, ravulizumab, or crovalimab at the labeled dose for at least 6 months 3. LDH persistently \> 1.5 × Upper Limit of Normal (ULN) in the previous 6 months that the Principal Investigator (PI) attributes is due to intravascular hemolysis 4. At least 2 screening LDH values from different visits as described in the protocol 5. 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 and agreement to continue to remain up to date with these vaccinations during the study Key Exclusion Criteria: 1. Receipt of an organ transplant, history of bone marrow transplantation or other hematologic transplants 2. Body weight \<40 kilograms at screening visit 3. Patients with a known or suspected C5 mutation that is refractory to their current C5i treatment as described in the protocol 4. Any active or ongoing infection within 2 weeks of screening or during the screening period or any recent infection as described in the protocol 5. Known hereditary complement deficiency Note: Other protocol-defined Inclusion/ Exclusion Criteria apply