This study will test how well a new medicine called concizumab works for participants who have haemophilia A or B with or without inhibitors. The purpose is to show that concizumab can prevent bleeds and is safe to use.

Participants will have to inject the study medicine every day under the skin with a pen-injector.

The study will last for at least 2 years and up to about 4 years. The length of time the participant will be in the study depends on if the study medicine will be available for purchase in their country.

Inclusion Criteria:

• Informed consent/assent obtained before any study-related activities. Study-related activities are any procedures that are carried out as part of the study, including activities to determine suitability for the study.

• Diagnosis of congenital severe haemophilia A (FVIII below 1%) or moderate/severe congenital haemophilia B (FIX (coagulation factor IX) below or equal to 2%), or congenital haemophilia with inhibitors.

• For arm 1 only: Male aged below 12 years of age at the time of signing informed consent.

• For arm 1 only: Patients with inhibitors (haemophilia A with inhibitors or haemophilia B with inhibitors)

  1. Patients with HAwI (haemophilia A with inhibitors) with historical medical records of a total of at least 26 weeks of on-demand treatment (On-demand or PPX treatment qualifying for this study is understood as patient-treatment solely for bleeds with intravenous coagulation factor-containing products) within the last 52 weeks prior to enrolment (For patients below 1 year of age that have been diagnosed with haemophilia <1 year prior to enrolment, historical medical records from time of diagnosis will suffice as long as medical records of a total of at least 26 weeks of relevant treatment is available).
  2. Patients with HBwI (haemophilia B with inhibitors) with historical medical records of a total of at least 26 weeks of on-demand treatment (On-demand or PPX treatment qualifying for this study is understood as patient-treatment solely for bleeds with intravenous coagulation factor-containing products) within the last 52 weeks prior to enrolment (For patients below 1 year of age that have been diagnosed with haemophilia <1 year prior to enrolment, historical medical records from time of diagnosis will suffice as long as medical records of a total of at least 26 weeks of relevant treatment is available).
  3. Patients with HBwI regardless of the regimen and duration of previous haemophilia treatment (On-demand or PPX treatment qualifying for this study is understood as patient-treatment solely for bleeds with intravenous coagulation factor-containing products)

• For arm 1 only: Patients without inhibitors (haemophilia A or haemophilia B)

  1. Patients with historical medical records of at least 52 weeks of on-demand treatment (On-demand or PPX treatment qualifying for this study is understood as patient-treatment solely for bleeds with intravenous coagulation factor-containing products; Surgery related PPX or short-term PPX (e.g., in relation to a severe bleed) is not allowed) during the last year prior to enrolment and with at least 3 documented treated bleeds (For participants less than (<) 2 years of age there is no limitation for number of documented treated bleeds in the medical history) during this period
  2. Patients with historical medical records of a total of at least 26 weeks of PPX (prophylaxis) treatment (On-demand or PPX treatment qualifying for this study is understood as patient-treatment solely for bleeds with intravenous coagulation factor-containing products) within the last 52 weeks prior to enrolment (For patients below 1 year of age that have been diagnosed with haemophilia <1 year prior to enrolment, historical medical records from time of diagnosis will suffice as long as medical records of a total of at least 26 weeks of relevant treatment is available)

• For arm 2 only: Male patients (regardless of age) previously treated with concizumab via compassionate use.

Exclusion Criteria:

• Known or suspected hypersensitivity to study intervention or related products.
• Known inherited or acquired coagulation disorder other than congenital haemophilia.
• Ongoing or planned Immune Tolerance Induction treatment.
• History of thromboembolic disease (aIncludes arterial and venous thrombosis including myocardial infarction, pulmonary embolism, cerebral infarction/thrombosis, deep vein thrombosis, other clinically significant thromboembolic events and peripheral artery occlusion.). Current clinical signs of or treatment for thromboembolic disease. Patients who in the judgement of the investigator are considered at high risk of thromboembolic events (Thromboembolic risk factors could include, but are not limited to, hypercholesterolemia, diabetes mellitus, hypertension, obesity, smoking, family history of thromboembolic events, arteriosclerosis, other conditions associated with increased risk of thromboembolic events).

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com