ABSTRACT
Purpose: We report the immunogenicity and safety of a third BNT162b2 vaccine in pediatric solid organ transplant recipients (pSOTRs). Method(s): Samples from pSOTRs (12-18 years) enrolled in our multicenter, observational study (COVID-19 Antibody Testing of Recipients of Solid Organ Transplants and Patients with Chronic Diseases) who received a third vaccine (V3) were analyzed for antibodies to SARS-CoV-2 spike protein receptor-binding domain, with a positive cutoff of >=0.8 and maximum titer of >2500 U/mL. Pre-V3 samples were 1-3 months after vaccine 2, and post-V3 were 1 month after vaccine 3. Result(s): Thirty-seven pSOTRs (46% heart, 24% liver, 27% kidney, 3% multi) received V3. Median (interquartile range [IQR]) age was 15 (14-16) years;42% were male and 78% white. pSOTRs were median (IQR) 9 (6-13) years from transplant. Four (11%) patients had prior SARS-CoV-2 infection. Antibody titers were positive in 26/37 (70%) patients pre-V3 and 32/37 (86%) post-V3 (Figure). Median (IQR) antibody titers were higher post-V3 (2500 [1581-2500] U/mL) than pre-V3 (211 [0.8-2500] U/mL) in paired analysis (p<0.001). 6/11 (55%) pSOTRs with negative pre-V3 titers seroconverted, with a post-V3 median (IQR) titer of 418 (132-1581) U/ mL. Transplant within 3 years was associated with negative post-V3 titer (p=0.037). Main side effects after V3 were pain (71%) and fatigue (50%). No patients reported allergic reaction, myocarditis, or rejection. One patient tested positive for SARSCoV- 2 between vaccines 2 and 3, with negative pre- and post-V3 titers. At time of first vaccine, this patient was transplanted a year ago, treated for rejection recently, and taking 3 immunosuppression agents including an antimetabolite. Conclusion(s): In this limited cohort, 86% of pSOTRs had a positive antibody response after three SARS-CoV-2 vaccines with no adverse events. Importantly, 55% of pSOTRs with prior negative response seroconverted post-V3, and 100% of pSOTRs with positive response increased their antibody titer or remained at maximum titer. Our preliminary results suggest the benefit of a third vaccine for adolescent pSOTRs based on antibody response;larger studies are needed to assess vaccine effectiveness.