Reindl-Schwaighofer R, Heinzel A, Mayrdorfer M, et al. - In kidney transplant recipients (KTRs), comparable results were seen with homologous and heterologous vaccination strategies for a third SARS-CoV-2 vaccine dose, with both mRNA and vector vaccines achieving seroconversion in more than one-third of kidney transplant recipients. However, due to the high rate of nonresponders post-third dose, further strategies to prompt an immune response in kidney transplant recipients are urgently required.

• After 2 doses of an mRNA vaccine in KTRs, fewer than 50% of them develop antibodies against the SARS-CoV-2 spike protein.

• In this randomized clinical trial, 197 KTRs (mean [SD] age, 61.2 [12.4] years; 82 [42%] women) who had not developed SARS-CoV-2 spike protein antibodies after 2 doses of an mRNA vaccine were administered mRNA (homologous) (BNT162b2 or mRNA-1273) or vector (heterologous) (Ad26COVS1) as a third dose of a SARS-CoV-2 vaccine.

• Post-third vaccine receipt, 39% of participants developed SARS-CoV-2 antibodies.

• Antibody response rate for the mRNA and vector vaccines was 35% and 42%, respectively, without statistically significant difference between groups.

• Neutralizing antibodies were present in only 22% of seroconverted patients.

• A higher frequency of local pain at the injection site was noted with a third dose of an mRNA vaccine vs the vector vaccine, while systemic symptoms were comparable between groups.

• Overall, good tolerability and safety of heterologous vaccination strategy with a vector-based vaccine was evident but this strategy was not significantly superior to the homologous mRNA-based strategy.