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