Rotavirus vaccination and incidence of type 1 diabetes: a population-based natural experiment.

AIMS/HYPOTHESIS: Environmental factors, including infections, have been suspected to influence the risk of type 1 diabetes. Studies of rotavirus vaccine and risk of type 1 diabetes have shown conflicting results. We took advantage of the rapid and high uptake of the rotavirus vaccine among infants in Norway as a natural experiment to study the potential association between rotavirus vaccination and type 1 diabetes incidence in Norway. METHODS: In this cohort study, we followed all children born in Norway during 2007-2019 from 6 months to 5 years of age for type 1 diabetes. In an interrupted time series analysis, we compared type 1 diabetes incidence in children born before compared with after introduction of the rotavirus vaccination programme in September 2014. RESULTS: Of 740,744 included children, 846 were diagnosed with type 1 diabetes between 6 months and 5 years of age. Our primary interrupted time series analysis showed an increasing trend after implementation of the rotavirus vaccination programme (relative HR 1.11 [95% CI 1.03, 1.20]), which was not significant after excluding birth cohorts from 2013-2015 to avoid potential herd immunity effects (relative HR 1.05 [95% CI 0.93, 1.18]). In a secondary analysis comparing fully vaccinated with non-vaccinated children, the adjusted HR was 1.17 (95% CI 0.78, 1.77). CONCLUSIONS/INTERPRETATION: This study found no evidence for a reduced risk of type 1 diabetes after introduction of rotavirus vaccination in infancy.