Influenza Vaccination Among Individuals With Type 1 Diabetes in Denmark: Coverage, Persistence, and Determinants, 2015–2022

AIMS: To investigate influenza vaccination coverage (IVC) and persistence with annual influenza vaccination among individuals with type 1 diabetes in Denmark and to identify clinical, demographic, and socioeconomic factors associated with vaccination status. MATERIALS AND METHODS: We conducted a nationwide, register-based cohort study of individuals aged 1-64 years with type 1 diabetes across the influenza seasons 2015-2022 in Denmark. Annual influenza vaccination status was assessed, and the cohort was stratified into age groups (1-18 and 19-64 years) according to age-specific vaccine recommendations. We investigated associations between non-vaccination/non-persistence and demographic, clinical, and socioeconomic factors using Poisson regression to compute adjusted relative risk (aRR). Persistence was defined as receipt of influenza vaccination in more than 80% of eligible seasons during follow-up. RESULTS: We identified 25 473 individuals with type 1 diabetes corresponding to 168 212 influenza seasons. In 2015/16, IVC was 5.6% in children and 18.3% in adults. IVC remained stable until a marked increase in 2021/22 (15.7% and 41.8%, respectively). In children, longer diabetes duration, HbA1c ≥ 53 mmol/mol, and residence in The North Denmark Region were associated with non-vaccination. In adults, male sex, younger age, shorter educational attainment, and HbA1c ≥ 53 mmol/mol were associated with non-vaccination. In both populations, factors associated with non-persistence were similar to those observed with non-vaccination. CONCLUSIONS: In Denmark, IVC among individuals with type 1 diabetes remains well below WHO targets, highlighting the need for targeted vaccination strategies. Sociodemographic and clinical factors associated with non-vaccination identify population groups where preventive efforts should be prioritised.