Study sample
A total of 124 adolescents with AIIRDs and 80 healthy adolescents, vaccinated with two doses of BNT162b2 mRNA vaccine, participated in the study (Table 1). Among the participants, 64 (54.6%) patients and 30 (37.5%) controls were also vaccinated with the third dose. Both patient and control groups had comparable gender distributions of 60% and 51% females, respectively (p=0.27). Adolescents with AIIRD were significantly older than controls, mean age 15.5 years (SD 1.99) compared with 13.7 years (SD 1.36), p<0.0001, respectively. JIA was the most common disease (n=54, 44%), followed by SLE (n=20, 16%). The mean disease duration was 4.12 years (SD. 3.79).
Most patients, n=92 (74%), were receiving immunomodulatory therapies (Table S1). Conventional synthetic DMARDs (csDMARDs) were used by 57 (45.9%) patients, with methotrexate and plaquenil the most frequent (n=27 (21.8%) and n=26 (21.1%), respectively), followed by mycophenolate mofetil (MMF) (n=13, 10.5%). Glucocorticoids were used by 21 (16.9%) patients, mean dose 11.6 mg/day (SD 11.88). Biologic DMARDs (bDMARDs) were used by 48 (38.7%) patients. TNF inhibitors (TNFi) were the most common bDMARD, used by 39 (31.5%) patients, followed by the IL-6 inhibitor (n=7, 5.7%) and CD-20 depleting therapy (rituximab (RTX); n=4, 3.2%). Janus kinase inhibitors were used by 5 (4%) patients.