ALXN1210 (Ravulizumab) Versus Eculizumab in Complement Inhibitor Treatment-Naïve Adult Participants With Paroxysmal Nocturnal Hemoglobinuria (PNH)

Criteria For Patient Cohort Originally Enrolled in ALXN1210-PNH-301 Study: Inclusion Criteria: 1. Male or female ≥18 years of age. 2. PNH diagnosis confirmed by documented by high-sensitivity flow cytometry. 3. Presence of 1 or more of the following PNH-related signs or symptoms within 3 months of screening: fatigue, hemoglobinuria, abdominal pain, shortness of breath (dyspnea), anemia (hemoglobin \<10 gram/deciliter), history of a major adverse vascular event (including thrombosis), dysphagia, or erectile dysfunction; or history of packed red blood cells (pRBC) transfusion due to PNH. 4. Lactate dehydrogenase (LDH) level ≥1.5 times the upper limit of normal at screening. 5. Documented meningococcal vaccination not more than 3 years prior to, or at the time of, initiating study treatment. 6. Female participants of childbearing potential must use highly effective contraception starting at screening and continuing until at least 8 months after the last dose of ravulizumab. 7. Willing and able to give written informed consent and comply with study visit schedule. Exclusion Criteria: 1. Treatment with a complement inhibitor at any time. 2. History of bone marrow transplantation. 3. Body weight \<40 kg. 4. Females who are pregnant, breastfeeding, or who have a positive pregnancy test at screening or Day 1. 5. Participation in another interventional clinical study or use of any experimental therapy within 30 days before initiation of study drug on Day 1 in this study or within 5 half-lives of that investigational product, whichever is greater. 6. History of or ongoing major cardiac, pulmonary, renal, endocrine, or hepatic disease that, in the opinion of the investigator or sponsor, would preclude participation. 7. Unstable medical conditions (for example, myocardial ischemia, active gastrointestinal bleed, severe congestive heart failure, anticipated need for major surgery within 6 months of randomization, coexisting chronic anemia unrelated to PNH). Eligibility Criteria For Roll-over Cohort: 1. All participants regardless of age, who are currently receiving ALXN1210 IV in an ongoing ALXN1210 study in patients with PNH 2. Participants must be willing and able to give written informed consent and to comply with all Extension study visits and procedures, including the use of any data collection device(s) to directly record patient data 3. Females of childbearing potential and male patients with female partners of childbearing potential must use highly effective contraception continuing until at least 8 months after the last dose of ravulizumab.