Background. Initial reports in adult kidney transplant recipients (KTR) indicate low immunogenicity after 2 doses of the BNT162b2 COVID-19 mRNA vaccine. We describe the immunogenicity of this vaccine compared to the serologic response in naturally infected COVID-19 positive adolescent and young adult KTR. Methods. For this prospective observational study, the study group included 38 KTR who received 2 doses of the tested vaccine, and the control group included 14 KTR who had a previous polymerase chain reaction–confirmed COVID-19 infection. Results. The mean age was 18 ± 3 y. Positive serologic responses were observed in 63% and 100% of the study and control groups, respectively ( P = 0.01). Antibody titers were almost 30-fold higher in the control than the study group (median [interquartile range (IQR)]: 2782 [1908–11 000] versus 100.3 [4.7–1744] AU/mL, P < 0.001), despite the longer time from the COVID-19 infection to serologic testing compared to time from vaccination (median [IQR]: 157.5 [60–216] versus 37 [20.5–53] d, P = 0.011). Among vaccinated patients, higher proportions of those seronegative than seropositive were previously treated with rituximab (50% versus 8%, P = 0.01). Time from the second vaccine dose to serologic testing was longer in seropositive than seronegative patients (median [IQR]: 24.5 [15–40] versus 46 [27–56] d, P = 0.05). No patient developed symptomatic COVID-19 disease postvaccination. Conclusions. The BNT162b2 COVID-19 mRNA vaccine yielded higher positive antibody response in adolescent and young adult KTR than previously reported for adult KTR. Antibody titers after vaccination were significantly lower than following COVID-19 infection. Longer time may be required to mount appropriate humoral immunity to vaccination in KTR.

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