Short- and Long-term Humoral Response of Immunosuppressed Children to SARS-CoV-2 BNT162b2 Vaccine

Introduction: This study aimed to evaluate in detail the short- and long-term humoral responses to the BNT162b2 (BioNTech, SE, Mainz, Germany/Pfizer Inc, New York, NY) vaccine in immunosuppressed children aged 5-11 years compared with healthy children. Methods: A prospective cohort study was conducted with immunosuppressed and healthy children 5-11 years of age following complete vaccination, defined as 3 doses of the BNT162b2 vaccine for immunosuppressed participants and 2 doses for healthy participants. The primary endpoints included IgG antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein and receptor-binding domain, as well as neutralizing capacity, 1- and 6-months postvaccination. Secondary endpoints included evaluations of breakthrough infections and cellular immune responses against SARS-CoV-2. Results: Thirty-five participants (20 healthy and 15 immunosuppressed) were included in the study. We could not demonstrate a different serological response in healthy children compared with immunosuppressed children in levels of anti-Spike IgG, anti-receptor-binding domain IgG, or neutralizing antibody at 1- and 6-months postvaccination. Humoral responses declined significantly by 6 months in healthy children; we could not demonstrate a significant decline in immunosuppressed children. Cellular immunity at 6 months showed a strong correlation with humoral response (R ≥ 0.74). Overall, the immunological response appeared protective for up to 6 months in both healthy and immunosuppressed participants, with only 1 breakthrough infection in a healthy child. Conclusions: After 3 vaccine doses, immunosuppressed children demonstrate 6-month immune comparable to healthy children who received 2 doses. Despite a decline in humoral responses over time, there were no infections, supporting the effectiveness of current coronavirus disease 2019 vaccination strategies.