To Örebro University

Introduction: Recent studies worldwide have reported an increased incidence of type 1 diabetes (T1D) during the COVID-19 pandemic in 2020-2022. Sweden adopted a distinct strategy bynot enforcing a strict lockdown, in contrast to other countries.

Objectives: The difference in public health strategy provides a unique opportunity to study potential effects on T1D. We aimed to investigate if there was a change in incidence rate during the pandemic in Sweden and to determine if clinical characteristics were affected in children diagnosed with T1D.

Methods: The incidence rate was calculated between 2018 and 2023 in children <18 years. Clinical differences were observed focusing on two groups: children diagnosed with T1D before (2018-2019) and during the pandemic (2021-2022). Year 2020 was considered a gap year since the pandemic began in March. Annual incidence data was obtained from the national Better Diabetes Diagnosis (BDD) study where >95% of all children with newly diagnosed T1D are registered. Clinical data was obtained from BDD and from the National Diabetes Register.

Results: Number of new yearly cases included in the Better Diabetes Diabetes (BDD) study per 100 000 children under 18 years of age in Sweden. More than 95% of children with newly diagnosed T1D in Sweden are registered in the BDD study. The incidence rate was 41.50/ 100.000/ year before the pandemic 2018-2019 and stayed the same in 2020 but increased by 17.0% to 48.55/ 100.000/ year in 2021-2022. A higher proportion of boys were diagnosed 2021-2022, they had an increased frequency of autoantibody negativity (p=0.002) and exhibited a different distribution of HLA genotypes compared to boys diagnosed before the pandemic with a decrease in DQ2/DQ8 and DQ2/DQX and a rise in DQ8/DQX and DQX/DQX (p=0.001). BMI in children diagnosed during the pandemic was higher compared to 2018-2019 (p=0.018), particularly in boys (p=0.05).

Conclusions: Our findings indicate that the pandemic affected the clinical characteristics of children diagnosed with T1D in Sweden and influenced the incidence rate of T1D. The increased incidence rate seemed to primarily reflect an increased incidence in boys. It is possible that boys were more susceptible to certain environmental triggers during the COVID-19 pandemic.