ABSTRACT
Background: Kidney transplant recipients are at high risk of mortality and complications related to COVID-19. Vaccination remains the most important strategy to prevent severe disease in this vulnerable population. The goal of this study was to evaluate the antibody response to mRNA vaccines in kidney transplant recipients. Method(s): We studied anti-spike IgG response to mRNA vaccines (BNT162b2 and mRNA-1273) against SARS-CoV-2 in adult kidney transplant recipients in a single center. Preserved blood samples of kidney transplant patients undergoing routine monitoring were used. The LABScreen COVID Plus Assay (One Lambda) was used to detect SARSCoV-2 antibody response. Categorical variables were compared using the Fisher's exact test, and continuous variables were compared using a t-test. Result(s): Among 120 subjects receiving two doses of vaccines, only 74 (61.7%) elicited a positive response with anti-Spike antibody. After a third dose/first booster vaccine, 35 out of 43 (81.4%) kidney subjects had a positive response. There was no statistically significant difference between the responders and non-responders in terms of age, gender, race, blood group, time since transplant, vaccine type. A third dose vaccine produced statistically significant increase in antibody response compared to 2 doses only. A third dose induced a serological response in 7 out of 8 subjects (87.5%) who did not respond after 2 doses of vaccine. None of the patients developed donor specific HLA antibody in response to COVID-19 infection or the vaccine. Conclusion(s): In this single center retrospective study, we demonstrated that the antibody response to SARS-CoV-2 mRNA vaccine was most prevalent after 4 months since the second dose. In addition, a third dose induced an antibody response in a larger number of kidney transplant recipients (81.3% vs 61.67%, p value 0.018), suggesting that this patient population may benefit from receiving multiple doses of mRNA vaccines.