A Research Study to Compare a New Weekly Insulin, Insulin Icodec, and an Available Daily Insulin, Insulin Degludec, Both in Combination With Mealtime Insulin in People With Type 1 Diabetes (ONWARDS 6)

This study compares insulin icodec (a new insulin) to insulin degludec (an insulin already available on the market) in people with type 1 diabetes. The study will look at how well insulin icodec taken weekly controls blood sugar compared to insulin degludec taken daily. Participants will either get insulin icodec that participants will have to inject once a week on the same day of the week, or insulin degludec that participants will have to inject once a day at the same time every day. Which treatment participants get is decided at random. Participants will also get a mealtime insulin. The insulin is injected with a needle in a skin fold in the thigh, upper arm or stomach. The study will last for about 1 year and 2 months. Participants will have 28 clinic visits and 28 phone calls with the study doctor. At 11 clinic visits participants will have blood samples taken. At 6 clinic visits participants cannot eat or drink (except for water) for 8 hours before the visit. Participants will be asked to wear a sensor that measures your blood sugar all the time. Participants will be asked to wear it for a total of 57 weeks (around 1 year). Women cannot take part if pregnant, breast-feeding or plan to become pregnant during the study period.