This study is researching a clinical treatment combination with two experimental drugs called pozelimab and cemdisiran. The study is focused on people with paroxysmal nocturnal hemoglobinuria (PNH). The aim of the study is to see how safe and effective the pozelimab + cemdisiran combination is for people with PNH and how the combination compares with 2 existing treatments: ravulizumab and eculizumab.

The pozelimab + cemdisiran combination may be referred to as "study drugs". Ravulizumab and eculizumab may also be called the "comparator drug".

The study is looking at several research questions, including:

• How effective is the pozelimab + cemdisiran combination compared to ravulizumab?
• How effective is pozelimab + cemdisiran combination compared to eculizumab?
• What side effects may happen from taking the study drugs?
• How much study drugs are in the blood at different times?
• Whether the body makes antibodies against the study drugs (which could make the study drugs less effective or could lead to side effects)

Key Inclusion Criteria:

1. Diagnosis of PNH confirmed by high-sensitivity flow cytometry testing with PNH granulocytes or monocytes as described in the protocol
2. Active disease, as defined by the presence of 1 or more PNH-related signs or symptoms as described in the protocol
3. LDH level ≥2 × ULN at the screening visit
4. 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:

1. 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
2. Receipt of an organ transplant, history of bone marrow transplantation or other hematologic transplant
3. Body weight <40 kilograms at screening visit
4. Planned use of any complement inhibitor therapy other than study drugs during the treatment period
5. 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 within 3 years prior to the screening visit as described in the protocol.
6. Any contraindication for receiving Neisseria meningitidis vaccinations (serotypes ACWY and B).
7. 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 quadrivalent meningococcal vaccine [serotype ACWY] or the second dose of the serotype B meningococcal vaccine [when available] is less than 2 weeks prior to study treatment initiation) as described in the protocol
8. 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
9. Documented history of active, uncontrolled, ongoing systemic autoimmune diseases

Note: Other protocol-defined Inclusion/ Exclusion Criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry),
• the legal authority to share the data, and
• ensured the ability to protect participant privacy.

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf