ABSTRACT
Background. Pediatric kidney transplant recipients (PKTR) are at risk of poor outcomes from COVID-19. Data on serologic responses to COVID-19 vaccines in PKTR remain sparse. We characterized the magnitude, breadth, and longevity of SARS-CoV-2 spike protein binding antibody responses in PKTR. Methods. This single institution, prospective observational study enrolled PKTR presenting to a transplant clinic for routine care who had received or were eligible to receive a COVID-19 vaccine. Demographic data, history of prior COVID-19, and vaccination details were collected. Plasma samples obtained from standard-of-care residual specimens were analyzed for SARS-CoV-2 spike variant IgG using the MesoScale Discovery V-PLEX platform, which quantitatively measures antibodies to SARS-CoV-2 full-length spike wild-type (Wuhan-hu-1), Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2), Gamma (P.1), and Omicron (B.1.1.529;BA.1) variants. Vaccine time points with > 5 samples available were analyzed. Geometric mean titers (GMTs) were calculated and log-transformed titers were compared using one-way ANOVA with Tukey's post-hoc comparisons test. Results. 61 PKTR enrolled (Table1);47 (77%) received at least 1 dose of COVID-19 vaccine in transplant clinic. 47 (77%) PKTR had at least one sample available for analysis, but serial specimens were lacking for many. By 6 months post-dose 2 of COVID-19 mRNA vaccination, spike (Wuhan-hu-1) IgG titers had waned to prevaccination levels (GMT 24 vs 47 binding antibody units (BAU)/mL, P=0.988). Administration of a 3rd dose of mRNA vaccine significantly boosted IgG antibodies (GMT 492 BAU/mL, P=0.007), and titers were maintained at 3 months (GMT 656 BAU/mL, P=0.001) but gradually waned by 6 months (GMT 223 BAU/mL, P=0.070). Administration of a 4th dose elicited a non-significant increase in titers (GMT 905 BAU/mL, P=0.870). Binding IgG antibodies to SARS-CoV-2 variant spike proteins post-vaccination were not significantly different from Wuhan spike. Conclusion. In this cohort of PKTR, a 3rd dose of COVID-19 mRNA vaccine significantly boosted broadly cross-reactive binding IgG antibodies to SARS-CoV-2 spike variants, including Omicron. Decreasing titers at 6 months post-dose 3 raise concern for waning protective immunity and support 4th dose vaccination.