Efanesoctocog Alfa Prophylaxis in Patients With Hemophilia A With Synovial Hypertrophy

Inclusion Criteria: Participant is diagnosed with moderate to severe hemophilia A (defined as less than or equal to (≤)5 percent (%) of endogenous FVIII clotting activity) at the time of consent/assent. Participant is more than or equal to (≥)12 years old at the time of consent/assent. Participant has existing synovial hypertrophy, defined as at least 1 eligible\* joint by the HEAD-US score (Synovitis score: 1 or 2) at the time of consent/assent. Participant has at least 1 eligible\* joint without planned future major orthopedic procedures (example, arthroscopic synovectomy, radioisotopic or chemical synoviorthesis), or major orthopedic procedures in the past 3 months prior to the screening visit (Visit 1). \*An eligible joint is a joint with existing synovial hypertrophy, as defined by a HEAD-US synovitis score of 1 or 2, considering hypertrophic synovium as an indication of the presence of synovitis Participant has received prophylactic treatment with hemophilia prophylaxis prescriptions in the last 12 months prior to the baseline visit (Visit 2). Participant is capable of understanding the written Informed Consent Form (ICF)/assent form, provides a signed and witnessed written ICF/assent form, and agrees to comply with the protocol requirements. If male, no contraceptive measures are required for this study. If female, is not pregnant or breastfeeding, and one of the following conditions applies: Is a women of nonchildbearing potential (WONCBP) Is a women of childbearing potential (WOCBP) and agrees to use a highly effective contraceptive method, with a failure rate of less than (\<)1 percent during the study treatment period (at least until the Week 52/ End of Treatment \[EoT\] visit). A WOCBP must have a negative serum pregnancy test at the screening visit (Visit 1) Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: Has other associated clotting disorders at the time of consent/assent. Is already under efanesoctocog alfa treatment. Has a current diagnosis of an factor VIII (FVIII) inhibitor, defined as inhibitor titer ≥0.60 BU/mL. Has ITI within the last 2 years prior to the baseline visit (Visit 2). Has been enrolled in a concurrent clinical interventional study or exposed to other investigational drug(s) within 3 months prior to screening for this study. Is currently in an institution because of regulatory or legal order (that is, is a prisoner or a patient who is legally institutionalized). Is not suitable for participation, whatever the reason, as judged by the investigator, including medical or clinical conditions, or patients potentially at risk of noncompliance to study procedures. Is an employee or family member of the investigator or site personnel. Is involved in a specific situation during study implementation or the course of the study that may raise ethics considerations. Has hypersensitivity to efanesoctocog alfa or its components or any of its excipients that, in the opinion of the investigator, contraindicates participation in the study.