Efanesoctocog Alfa Prophylaxis in Patients With Hemophilia A With Synovial Hypertrophy

The objective of the study is to assess the improvement of synovial hypertrophy during the 12 months of efanesoctocog alfa prophylaxis once per week (QW) in joints with existing evidence of synovial hypertrophy in participants with hemophilia A. The study duration for each participant is approximately 12 months.

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 WOCBP and agrees to use a highly effective contraceptive method, with a failure rate of less than (\