This study is investigating how Mim8 works compared to other medicines in people with haemophilia A, who either have inhibitors or do not have inhibitors. Mim8 is a new medicine that will be used for prevention of bleeding episodes. Mim8 works by replacing the function of the missing clotting factor VIII (FVIII).

When and how often participants will receive Mim8 is dependent on their previous treatment - but is otherwise decided by chance. Mim8 will be injected into a skinfold on the stomach with a thin needle either once a week or once a month.

The study will last 54-124 weeks (12-29 months) depending on how long participants will be followed in run-in before they start treatment and if they continue in the follow period or transfer to an open label extension study. Participants will have 12-17 clinic visits.

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 suitability for the study.
2. Male or female participants with diagnosis of congenital haemophilia A of any severity based on medical records.
3. Participant has been prescribed treatment with factor VIII concentrates or bypassing agent in the last 26 weeks prior to screening.
4. Age above or equal to 12 years at the time of signing informed consent.
5. Body weight greater than or equal to 30 kg.
6. Applicable to participants treated with on-demand/no prophylaxis prior to enrolment: ≥5 bleeds in the last 26 weeks prior to screening visit, for which factor VIII concentrates or bypassing agent has been prescribed.
7. Applicable to participants with FVIII activity ≥1% who are on prophylactic treatment: ≥1 bleed in the last 26 weeks prior to screening visit, for which factor VIII concentrates or bypassing agent has been prescribed.
8. Willingness and ability to comply with scheduled visits and study procedures, including the completion of diary and patient-reported outcomes questionnaires.

Exclusion Criteria:

1. Previous participation in this study. Participation is defined as signed informed consent.
2. Participation (i.e., signed informed consent) in any interventional clinical study with receipt of the last dose within 6 months (or 5 half-lives of the investigational medicinal product, whichever is shorter) before planned randomisation.
3. Exposure to non-factor haemostatic products for bleeding prophylaxis within 6 months (or 5 half-lives of the medicinal product, whichever is shorter) before planned randomisation, for participants not included in the run-in.
4. Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using a highly effective contraceptive method. Breast feeding is allowed only during the run-in period.
5. Any disorder, except for conditions associated with haemophilia A, which in the investigator's opinion might jeopardise participant's safety or compliance with the protocol.
6. Known or suspected hypersensitivity to trial product(s), any constituents of the product or to related products.
7. Receipt of gene therapy at any given time point.
8. Ongoing or planned immune tolerance induction (ITI) therapy.
9. Major surgery planned to take place after screening.
10. Known congenital or acquired coagulation disorders other than haemophilia A.
11. Hepatic dysfunction defined as aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) above 3 times the upper limit combined with total bilirubin above1.5 times the upper limit measured at screening.
12. Renal impairment defined as estimated Glomerular Filtration Rate (eGFR) below or equal to 30 ml/min/1.73 m^2 for serum creatinine measured at screening.
13. Previous or current thromboembolic disease or events (with the exception of previous catheter-associated thrombosis for which anti-thrombotic treatment is not currently ongoing) or risk of thromboembolic disease, as evaluated by investigator.
14. Mental incapacity, unwillingness to cooperate, or a language barrier precluding adequate understanding and cooperation.
15. Other conditions (e.g., autoimmune disease) or laboratory abnormality that may increase risk of bleeding or thrombosis as evaluated by the investigator.

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