Comparison of Humoral Response in Kidney Transplant Recipients and Donors and Healthy Volunteers Following Second Dose of SARS-CoV-2 mRNA Vaccine

Purpose. To investigate the kinetics and durability of anti-spike glycoprotein (S) immuno-globulin G (IgG) after the second dose of mRNA-based SARS-CoV-2 vaccine in kidney trans-plant recipients (recipients) compared with those in kidney donors (donors) and healthy volunteers (HVs) and identify factors negatively associated with SARS-CoV-2 vaccine effective-ness in recipients.Methods. We enrolled 378 recipients with no history of COVID-19 and no anti-S-IgG before the first vaccine and who received a second mRNA-based vaccine dose. Antibodies were detected using an immunoassay more than 4 weeks after the second vaccine dose. Anti-S-IgG <0.8, >= 0.8 to 15, and >= 15 U/mL were considered negative, weak positive, and strongly positive, respectively, whereas anti-nucleocapsid protein IgG was negative. Anti-S-IgG titer was deter-mined in 990 HVs and 102 donors.Results. Anti-S-IgG titers were 154, 2475, and 1181 U/mL in the recipient, HV, and donor groups, respectively, with values significantly lower in recipients. The anti-S-IgG-positivity rate of recipients gradually increased following the second vaccination, suggesting that recipients had a delayed response compared with the HV and donor groups, who had a 100% positivity rate at an earlier time point. Anti-S-IgG titers decreased in donors and HVs, whereas they remained stable in recipients, although at a significantly lower level. Independent negative fac-tors associated with anti-S-IgG titers in recipients were age >60 years and lymphocytopenia (odds ratio: 2.35 and 2.44, respectively).Conclusions. Kidney transplant recipients demonstrate delayed and attenuated responses, with lower SARS-CoV-2 antibody titers after the second dose of the mRNA-based COVID-19 vaccine.