LAUSR

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).