Kidney transplant recipients (KTRs) are extremely vulnerable to SARS‐CoV‐2 infection and show an impaired immune response to SARS‐CoV‐2 vaccination. We analyzed factors related to vaccination efficiency in KTRs. In a multicenter prospective observational study (NCT04743947), IgG antibodies levels against SARS‐CoV‐2 spike S1 subunit and their neutralization capacity after SARS‐CoV‐2 vaccination were analyzed in 225 KTRs and compared to 176 controls. After the vaccination, 56 (24.9%) KTRs became seropositive of whom 68% had neutralizing antibodies. This immune response was significantly lower compared to controls (239 [78–519] BAU/ml versus 1826 [560–3180] BAU/ml for KTRs and controls, p < .0001). The strongest predictor for an impaired response was mycophenolate mofetil (MMF) treatment. Multivariate regression analysis revealed that MMF‐free regimen was highly associated with seroconversion (OR 13.25, 95% CI 3.22–54.6; p < .001). In contrast, other immunosuppressive drugs had no significant influence. 187 out of 225 KTRs were treated with MMF of whom 26 (13.9%) developed antibodies. 23 of these seropositive KTRs had a daily MMF dose ≤1 g. Furthermore, higher trough MMF concentrations correlated with lower antibody titers (R −0.354, p < .001) supporting a dose‐dependent unfavorable effect of MMF. Our data indicate that MMF dose modification could lead to an improved immune response.

Background: Kidney failure patients on dialysis or after renal transplantation have a high risk for severe COVID-19 infection and vaccination against SARS-CoV-2 is the only expedient prophylaxis. Generally, immune responses are attenuated in kidney failure patients, however, systematic analyses of immune responses to SARS-CoV-2 vaccination in dialysis patients and in kidney transplant recipients (KTR) are still missing. Methods: In this prospective multicentric cohort study, antibody responses COVID-19 mRNA vaccines (BNT162b2; Biontech/Pfizer or mRNA-1273; Moderna) were measured in 32 dialysis patients and in 28 KTRs. SARS-CoV-2-specific antibodies and neutralization capacity were evaluated and compared to controls (n=78) in a similar age-range. Results: After the first vaccination, SARS-CoV-2-specific antibodies were nearly undetectable in kidney failure patients. After the second vaccination, 93% of the controls and 88% of dialysis patients but only 37% of KTRs developed SARS-CoV-2-specific IgG above cut-off. Moreover, mean IgG levels were significantly lower in KTRs (54±93 BAU/ml) compared to dialysis patients (503±481 BAU/ml, p<0.01). Both KTRs as well as dialysis patients had significantly lower IgG levels compared to controls (1992±2485 BAU/ml; p<0.001 and p<0.01). Importantly, compared to controls, neutralizing antibody titers were significantly lower in KTRs and dialysis patients. After the second vaccination, 76% of KTRs did not show any neutralization capacity against SARS-CoV-2 suggesting impaired seroprotection. Conclusions: Kidney failure patients show a significantly weaker antibody response compared to controls. Most strikingly, only one out four KTRs developed neutralizing antibodies against SARS-CoV-2 after two doses of vaccine. These data suggest that vaccination strategies need modification in immune transplant and dialysis patients.

Modification of vaccination strategies is necessary to improve the immune response to SARS‐CoV‐2 vaccination in kidney transplant recipients (KTRs). This multicenter observational study analyzed the effects of the third SARS‐CoV‐2 vaccination in previously seronegative KTRs with the focus on temporary mycophenolate mofetil (MMF) dose reduction within propensity matched KTRs. 56 out of 174 (32%) previously seronegative KTRs became seropositive after the third vaccination with only three KTRs developing neutralizing antibodies against the omicron variant. Multivariate logistic regression revealed that initial antibody levels, graft function, time after transplantation and MMF trough levels had an influence on seroconversion ( P < .05). After controlling for confounders, the effect of MMF dose reduction before the third vaccination was calculated using propensity score matching. KTRs with a dose reduction of ≥33% showed a significant decrease in MMF trough levels to 1.8 (1.2–2.5) μg/ml and were more likely to seroconvert than matched controls ( P = .02). Therefore, a MMF dose reduction of 33% or more before vaccination is a promising approach to improve success of SARS‐CoV‐2 vaccination in KTRs.