SARS-CoV-2 infection and COVID-19 vaccination and the risk for new-onset type 1 diabetes: a register-based population study in Sweden

Abstract Aims/hypothesis Reports from several countries suggested increased incidence of type 1 diabetes during the COVID-19 pandemic, but causality has remained unclear. We investigated incident type 1 diabetes related to SARS-CoV-2 infection and vaccination in Swedish children and adults and assessed whether vaccination modified infection-related risk. Methods We assembled a register-based cohort of all residents aged 0.5). When vaccination was investigated as the exposure, children showed lower HRs (0.77; 0.67, 0.88) within 2 years, but this association was not observed in ages 12–17 (1.00; 0.80, 1.26); adults showed a small excess risk within 0–30 days after dose 1 (1.32; 1.07, 1.62), but not in later windows or doses. Conclusions/interpretation Short-term elevations in incident type 1 diabetes diagnoses were observed in the first 30 days after infection and after first vaccination, and did not persist, supporting detection/diagnostic acceleration rather than a sustained causal effect of SARS-CoV-2 infection or vaccination on type 1 diabetes.