Humoral response and safety of BNT162b2 mRNA vaccine in children with rheumatic diseases.

OBJECTIVES: The coronavirus disease 2019 (COVID-19) vaccine represents a cornerstone in tackling the pandemic and with the approval of the BNT162b2 mRNA vaccine in December 2020, it has become a beacon of hope for people around the world, including children. This study aimed to present the data on the humoral response and safety of vaccine in a cohort of patients with paediatric rheumatic diseases receiving immunomodulatory treatments. METHODS: Forty-one children with paediatric rheumatic diseases were included and were vaccinated with the BNT162b2 mRNA vaccine (two doses of 30 µg administered 3-4 weeks apart). To assess the humoral response, IgG antibodies developed against the S1/Receptor-binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein at baseline and 3-4 weeks after the second dose were measured. The possible local and systemic side effects and disease activity scores were evaluated during the study period. RESULTS: After the second dose of vaccine, markedly elevated anti-RBD IgG titres were observed in all patients with a median titre of 20 474 AU/ml [interquartile range (IQR) 6534-36 151] with a good safety profile. The median disease duration was 4.3 (IQR 3.5-5.6) years. In the cohort, 14 (34.1%) received conventional DMARDs (cDMARDs), 16 (39%) received biologic DMARDs (bDMARDs) and 11 (26.8%) received a combined therapy (cDMARDs and bDMARDs). Patients treated with combined therapy [median 4695 (IQR 2764-26 491)] had significantly lower median titres of anti-RBD IgG than those receiving only cDMARDs. CONCLUSION: Paediatric rheumatic diseases patients receiving immunomodulatory treatments were able to mount an effective humoral response after two dose regimens of BNT162b2 mRNA vaccine safely without interrupting their current treatments.