Immunogenicity following an additional dose of Coronavirus disease 2019 (COVID-19) vaccine was investigated in an extended primary series among kidney transplant (KT) recipients. Eighty-five KT participants were randomized to receive either an mRNA (M group; n =??43) or viral vector (V group; n =??42) vaccine. Among them,62% were male,with a median (IQR) age of 50 (43-59) years and post-transplantation duration of 46 (26-82) months. At 2??weeks post-additional dose,there was no difference in the seroconversion rate between the M and V groups (70% vs. 65%,p =??.63). A median (IQR) of anti-RBD antibody level was not statistically different between the M group compared with the V group (51.8 [5.1-591] vs. 28.5 [2.9-119.3] BAU/ml,p =??.18). Furthermore,the percentage of participants with positive SARS-CoV-2 surrogate virus neutralization test results was not statistically different between groups (20% vs. 15%,p =??.40). S1-specific T cell and RBD-specific B cell responses were also comparable between the M and V groups (230 [41-420] vs. 268 [118-510],p =??.65 and 2 [0-10] vs. 2 [0-13] spot-forming units/106 peripheral blood mononuclear cells,p =??.60). In conclusion,compared with an additional dose of viral vector COVID-19 vaccine,a dose of mRNA COVID-19 vaccine did not elicit significantly different responses in KT recipients,regarding either humoral or cell-mediated immunity. (TCTR20211102003).
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