Type 1 diabetes was more common during the COVID-19 pandemic, according to observational research; however, there is still conflicting data connecting it to SARS-CoV-2 infection. Furthermore, there is disagreement about whether the COVID-19 vaccine has protective or triggering effects. This study examines how SARS-CoV-2 infection and COVID-19 vaccinations affect the risk of new-onset type 1 diabetes in children and adults because there is a dearth of evidence on adult-onset cases.
Researchers created a register-based cohort that included inhabitants under 80 years old on January 1, 2020, as well as births throughout the follow-up period (1 January 2020-December 31, 2023). The risk windows following infection (and after each vaccination dosage) were 0-30 days, 31-180 days, 181-365 days, and 1-2 years. Incident type 1 diabetes was defined as the earliest ICD-10 diagnosis E10 in the National Diabetes Register or the National Patient Registry. Cox regression using calendar time as the timeframe was employed with time-varying exposures. The analyses were stratified by age (children <18 years; adults 18-79 years) and age-appropriate covariate adjustment. Children's sensitivity analyses were limited to the ages of 12 to 17.
There were 6,870,328 adults (4453 incident type 1 diabetes) and 2,650,492 children (3813 incident type 1 diabetes) in the cohort. In children (hazard ratio [HR] 1.22; 95% confidence interval 1.10, 1.36) and adults (1.10; 1.00, 1.20), SARS-CoV-2 infection was linked to an elevated risk of type 1 diabetes within two years. This association was mostly driven by the 0–30-day window (5.41; 4.34, 6.74 in children, 3.33; 2.69, 4.12 in adults).
The risk of infection was not altered by vaccination (interaction p>0.5). Children showed lower HRs (0.77; 0.67, 0.88) within two years when vaccination was examined as the exposure, but this association was not seen in ages 12–17 (1.00; 0.80, 1.26); adults showed a slight excess risk within 0–30 days after dose 1 (1.32; 1.07, 1.62), but not in later windows or doses.
Overall, in the first 30 days following infection and the first vaccine, this study saw brief increases in incidence of type 1 diabetes diagnoses; however, these increases did not last.
Reference:
Li, H., Morris, L., Bygdell, M., Santosa, A., Allansson Kjölhede, E., Eeg-Olofsson, K., Nyberg, F., & Xu, Y. (2026). SARS-CoV-2 infection and COVID-19 vaccination and the risk for new-onset type 1 diabetes: a register-based population study in Sweden. Diabetologia. https://doi.org/10.1007/s00125-026-06767-6
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