A Study to Assess the Efficacy and Safety of Emicizumab in Participants With Type 3 Von Willebrand Disease

This is a Phase III, multicenter, open-label clinical study designed to evaluate the efficacy, safety, pharmacokinetics, and pharmacodynamics of emicizumab prophylaxis in participants aged 1 month and above, who have been diagnosed with Type 3 von Willebrand disease (VWD). Participants on prior standard of care (SOC) on-demand therapy will be assessed via a randomized comparison (Arm A - emicizumab prophylaxis and Arm B - continuation of SOC on-demand therapy), while participants on prior SOC prophylactic therapy (Arm C - emicizumab prophylaxis) will be assessed via intra-participant analysis with data obtained from the preceding non-interventional study (NIS), WP45335 (NCT06883240).

Inclusion Criteria: * Confirmed diagnosis of Type 3 von Willebrand disease (VWD), based on medical records * Preexisting medical record verifying the status of von Willebrand factor (VWF) inhibitor (positive or negative, including titer if available) * Adequate hematologic, hepatic, and renal function * For participants of childbearing potential: agreement to remain abstinent or adhere to the contraception requirements Additional Inclusion Criteria for Arms A and B: * Age ≥1 month at the time of signing Informed Consent/Assent Form * Documented previous use of on-demand therapy with intermittent (less than once a week) on-demand SOC therapy for VWD * Having ≥2 treated bleeds (except menstrual bleeds) with factor concentrate within 24 weeks prior to enrollment Additional Inclusion Criteria for Arm C: * Age ≥2 years at the time of signing Informed Consent/Assent Form * Documented and confirmed previous use of SOC prophylactic therapy for VWD (1-3 times weekly, as per prescribed dose) as described in the eligibility of Study WP45335 * Have completed all study requirements as defined in the WP45335 protocol for at least 24 weeks Exclusion Criteria: * Inherited or acquired bleeding disorder other than Congenital Type 3 VWD * History of gastrointestinal bleeding within 18 months prior to enrollment, or any previous diagnosis of angiodysplasia * History of intracranial hemorrhage * Previous or current treatment for thromboembolic disease or signs of thromboembolic disease * Other conditions (e.g., certain autoimmune diseases) that may increase risk of bleeding or thrombosis * History of clinically significant hypersensitivity associated with monoclonal antibody therapies or components of the emicizumab injection * Use of systemic immunomodulators (e.g., interferon) at enrollment or planned use during the study, with the exception of anti-retroviral therapy