Study population
The study population included adolescents (ages 12–18 years) with juvenile-onset of the following AIIRDs: JIA according to the EULAR 2001 classification criteria; systemic lupus erythematosus (SLE) according to the 1997 ACR or 2012 SLICC criteria; systemic vasculitis, i.e. ANCA-associated vasculitis (AAV), including granulomatosis with polyangiitis (GPA), according to the Chapel Hill Consensus Conference definitions; Behçet’s disease, idiopathic uveitis, IBD-related arthritis, systemic or localized scleroderma or juvenile dermatomyositis according to the EULAR/ACR classification criteria; or autoinflammatory syndromes. Patients were instructed to continue all medications during the vaccination period. Patients were recruited from four medical centres, including 97 (78%) participants from Israel and 27 (22%) from Slovenia. The control group consisted of healthy adolescent volunteers recruited by Dana Dwek Children’s Hospital, who provided blood samples during a well-being visit. Exclusion criteria were previous COVID-19 infection and for controls, history of an AIIRD or immunosuppressive treatment.
All study participants were vaccinated with two doses of BNT162b2 mRNA vaccine (30 μg per dose, administered intramuscularly, 3 weeks apart). The third vaccine dose was administered at least 6 months after the first vaccine dose, as indicated by the national guidelines of Israel.