This is a 48-month observational, prospective, multicentre study. The overall aim of the study is to evaluate the long-term effectiveness of Elocta treatment on joint health in patients treated prophylactically with Elocta in a real-world setting.

Haemophilia A is a rare genetic disorder estimated to occur in one out of 10,000 live births, characterized by a deficiency in coagulation factor VIII causing impaired haemostasis and prolonged bleeding episodes. Moderate haemophilia, defined as < 5%, and severe haemophilia, defined as < 1% of normal factor VIII activity result in frequent and spontaneous bleeds into muscles and joints, commonly the elbows, knees, and ankles. Bleeding into joints can cause acute pain and swelling and can result in reduced joint range of motion, long-term cartilage damage and debilitating haemophilic arthropathy. Early use of prophylaxis with factor VIII replacement is recommended following diagnosis of haemophilia A to maintain joint health and prevent joint destruction. However, despite the use of prophylaxis many patients still experience joint bleeds which may lead to joint deterioration over time. The risk of joint bleeds increases with the amount of time spent below certain FVIII trough levels, e.g. 1, 3 or 5 IU/dL. Thus, there is probably a relation between the intensity of the prophylactic treatment regimen and joint health. Elocta is an extended half-life rFVIII product (EHL rFVIII), with a slower clearance as compared to conventional FVIII products. Treatment with Elocta will therefore provide the treater with a greater flexibility for individualizing prophylaxis as compared to conventional FVIII. Higher trough levels can be reached with Elocta without increasing factor usage or injection frequency. The treater can instead choose to reduce the injection frequency or the factor consumption without lowering trough levels.

Patients may limit their physical activities due to fear of bleeding if they are unaware of their current FVIII level. Patient apps and wearables are now available which allow patients to view their predicted FVIII levels, and capture health-related data (such as bleedings, pain, well-being, physical activity levels etc.). This data can be shared with the treating physician supporting the planning to individualize the patient's factor treatment based on current lifestyle, health status and physical activity levels. Florio, a certified medical device used as part of routine clinical practice, is such an app, and the data output and patient feedback on their activity levels and sense of protection while using Florio will be analysed as exploratory objectives in this study.

The main purpose of this study is to evaluate the effectiveness of Elocta on joint health over a long observation period (48 months). The study will also explore the influence on long term joint health of different Elocta prophylaxis regimens leading to different trough levels and if the extent of patients' physical activity levels can be associated with predicted FVIII levels.

Inclusion Criteria:

• Provided signed and dated informed consent by the patient, or the patient's legally authorized representative(s) for patients under the legal age, before any study-related activities are undertaken. Assent should be obtained from paediatric patients according to local regulations
• Have a diagnosis of haemophilia A
• At enrolment on prophylactic treatment with Elocta, independent of participation in the study

Exclusion Criteria:

• Enrolment in another concurrent clinical interventional study, or intake of an Investigational Medicinal Product (IMP), within three months prior to inclusion in this study
• Presence of factor VIII antibodies (inhibitors) (≥0.60 Bethesda Unit [BU]/mL) at the latest available inhibitor test

Patients diagnosed with haemophilia A regardless of severity, of any gender and age, on factor treatment with Elocta according to usual clinical practice.