This study will collect data on bleeds and data related to quality of life in people with severe congenital (a disease existing from birth) haemophilia A and B, with or without inhibitors. The aim for the study is to look at the number of bleeds when on usual treatment for haemophilia. Participants will be asked to keep an electronic diary to track the number of bleeds and the treatment of their bleeds. Participants will be asked to wear an activity tracker on their wrist to capture their level of activity every day for up to 12 weeks. While taking part in this study, participants will keep getting their usual treatment as given to them by their doctor. All study visits at the clinic are done in the same way as the participants are used to. In the time between the participants' visits to the clinic, the study staff at the clinic may call or email the participant. The study will last for about 2½ years.

Inclusion Criteria:

1. Informed consent 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 eligibility for the study.

2. Male, age equal to or above 12 years at the time of signing informed consent.

3. Patients with congenital haemophilia with inhibitors treated with FEIBA® prophylaxis: equal to or above 2 treated bleeding episodes within 24 weeks before screening (visit 1).

   (For Turkey only: Patients with congenital haemophilia with inhibitors treated with by-passing agents prophylaxis: equal to or above 2 treated bleeding episodes within 24 weeks before screening (visit 1)).

4. Severe (FVIII activity below 1%) congenital haemophilia A or severe/moderate (FIX activity equal to or below 2%) congenital haemophilia B, or congenital haemophilia A or B of any severity, with a presence or history of inhibitor (equal to or above 0.6 Bethesda Unit (BU)), based on medical records

5. Patients with CHwI treated on-demand: equal to or above 6 treated (with bypassing agent) bleeding episodes within 24 weeks (or equal to or above 12 during 52 weeks) before screening (visit 1) and patients with severe congenital HA/HB treated on-demand: equal to or above 5 treated (with factor product) bleeding episodes within 24 weeks (or equal to or above 10 during 52 weeks) before screening (visit 1).

Exclusion Criteria:

1. Known or suspected hypersensitivity to monoclonal antibodies.
2. Previous participation in this study. Participation is defined as signed informed consent.
3. Any disorder, except for conditions associated with congenital haemophilia, which in the physician's opinion might jeopardise patient's safety or compliance with the protocol.
4. Previous treatment with concizumab. Previous treatment is defined as two or more doses administered.
5. Planned FVIII/FIX Immune Tolerance Induction (ITI) regimens during the study.
6. Current or planned treatment with emicizumab.
7. Any known congenital or acquired coagulation disorder other than congenital haemophilia.
8. History of thromboembolic disease, current clinical signs of or treatment for thromboembolic disease, or at high risk of thromboembolic disease as judged by the investigator.
9. Presence or history of malignant neoplasm within 5 years prior to the day of screening.

Patients with haemophilia A or B and with or without inhibitors

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