Association between Covid-19 BNT162b2 vaccination or SARS-CoV-2 infection and immune mediated diseases in 5 million 5-to-19-year-olds in four Nordic countries

BackgroundWe investigated new onset of autoimmune hepatitis (AH), Guillain-Barre syndrome (GBS) and Type 1 Diabetes (T1D), and potential increased disease activity (measured as recurrent hospital visits) of Juvenile Rheumatoid Arthritis (JRA), Multiple Sclerosis (MS) and T1D, following BNT162b2 vaccination or SARS-CoV-2 infection in children and adolescents. MethodsWe used nationwide data from Norway, Denmark, Finland, and Sweden, using 28- and 180-days risk periods following BNT162b2 vaccination or a positive test for SARS-Cov-2 infection. Individuals aged 5-19 years during the study period (1st January 2021-31st December 2022) were included. We used a common data model, using individual level data linked from nation-wide registers and a shared analysis script to harmonize data and analysis. Poisson regression was used to estimate relative risks (RRs) comparing outcome rates in risk windows to unvaccinated or uninfected follow-up rates. This was supplemented with self-controlled case series analyses. Results from different countries were analyzed jointly in a meta-analysis. ResultsWe observed no clear association between BNT162b2 vaccination and new-onset AH, GBS or T1D. Neither did we observe any clear association with recurrent hospital visits following BNT162b2 vaccination or SARS-CoV-2 infection. An association between SARS-CoV-2 infection and GBS was observed in both the 28-day and 180-day risk window (relative risk (RR) 15.10, 95% CI, 1.11-205.94, and RR 3.85, 1.33-11.14, respectively). ConclusionsBNT162b2 vaccination was not associated with new-onset or recurrent hospital visits of these diseases in children and adolescents. Sars-CoV-2 infection was associated with new-onset GBS. Estimates were however uncertain due to the small number of cases.