Notwithstanding the wealth of literature on COVID-19, studies focusing on young adults with autoimmune diseases (AD) are lacking. To determine early (within 7 days) and late (after 7 days) anti-SARS-CoV-2 vaccine-related adverse events (AEs), post-vaccine disease flares, COVID-19 severity and breakthrough infections (B-INFs) in young people with rheumatic diseases (RMDs) and non-rheumatic autoimmune diseases (nr-ADs) compared to healthy controls (HC). Data were captured through the international COVID-19 vaccination in autoimmune diseases (COVAD) 1 and 2 questionnaires. Of 20,685 complete responses, we identified 6010 from patients aged 18-35 years (1692 RMD, 400 nrADs, 3918 HC) who received up to 4 vaccine doses. BNT162b2 was the most frequently administered vaccine and prior to vaccination, 7% of people with nrAD were taking immunosuppressants (IS) versus 80% in RMDs. Early mild AEs were more frequent in RMDs (93%) and nr-ADs (92%) compared to HC (85%). The frequency of late mild AEs was < 20% in all groups. Severe AEs were rare. SARS-CoV-2 infection rates were similar across all groups, however, RMD patients reported a single episode of infection more frequently than nrADs and HC, while nrADs reported multiple infections more frequently than RMD. Self-reported disease flares were reported by 10% or RMD and 7% of nrAD patients. Our study reinforces the safety of anti-SARS-CoV-2 vaccine also in young people with ADs, but it also highlights that among young individuals the number and clinical picture of SARS-CoV-2 infections is affected more by the type of AD rather than by coexisting IS therapy.

COVID-19 severity, breakthrough infections and vaccine safety in young individuals with autoimmune diseases: insights from the COVAD study