Growing evidence shows diminished response to mRNA-based SARS-CoV-2 vaccination in kidney transplant recipients. We aimed to investigate the seroconversion rate after a 3rd and 4th dose of mRNA vaccination in kidney transplant recipients without prior antibody response to two or three vaccination doses. This retrospective study included 324 prevalent kidney transplant recipients of a single tertiary transplantation center of which 157 remained seronegative, defined as anti-spike-RBD-IgG antibody titer < 7.1 BAU/ml, after two doses of mRNA-based SARS-CoV-2 vaccination. Maintenance immunosuppression was not changed. The median patient age was 60.6 years (IQR 51.4-68.1 years), 66.9% were male. Positivity for anti-spike-RBD-IgG (≥ 7.1 BAU/ml) was measured 4-5 weeks after administration of a 3rd and 4th vaccine dose. Seroconversion rates were 63.9% after a 3rd dose and 29.3% after a 4th dose of vaccine. Cumulative preva-

Dear Editors, Kidney transplant recipients are at high risk for severe COVID-19 disease or death in case of SARS-CoV-2 infection (1). There is growing evidence suggesting that anti-SARS-Cov2-antibody response is markedly blunted in kidney transplant patients after vaccination (2). Severe COVID-19 and COVID-19-related death has been recently reported in kidney transplant recipients despite prior complete (two dose) vaccination with SARS-CoV-2 mRNA vaccines (3). (4).In this retrospective cohort study involving 320 prevalent kidney transplant recipients from a single transplant center (Ordensklinikum Linz-Elisabethinen hospital), anti-Spike (S) protein IgG antibody titers were measured 3-6 weeks [BNT162b2: median 28 days (IQR: 6 days), mRNA1273: median 28 days (IQR: 8 days)] after administration of the second dose of either mRNA-1273 or BNT162b2 SARS-CoV-2 vaccine. Vaccinations took place between January 15th and June 8th, 2021 according to the Austrian national SARS-CoV-2 vaccination program. Vaccine doses were allocated by the Austrian government depending on availability. Patients were vaccinated ranked by age beginning with the oldest as soon as vaccines were available. Allocation to a certain vaccine (BNT162b2 or mRNA-1273) was therefore determined by the vaccination progress in our kidney transplant cohort and vaccine availability at that time. A two-dose vaccination regimen was applied, with 3-weeks (BNT162b2) and 4-weeks (mRNA-1273) intervals between the first and second vaccination, regardless of a history of prior infection with SARS-CoV-2.Anti-SARS-CoV-2-antibodies directed against the receptor binding domain (RBD) of the S1 subunit of the Spike (S) protein were measured with the SARS-CoV-2 IgG II Quant assay (Abbott Ireland Diagnostics Division, Finisklin Business Park, Sligo, Ireland), which was reported to have high sensitivity and specificity for detection of anti-SARS-CoV-2 S-protein antibodies (5) and high correlations with anti-SARS-CoV-2 neutralizing antibodies (6). Results were reported in BAU/ml (binding antibody units). Differences between vaccine groups (mRNA-1273 vs BNT162b2) in S-antibody-positivity were tested for statistical significance using the Chi 2 -Test. To further investigate the impact of vaccine type on S-antibody-positivity, we computed a multivariate logistic regression model taking potential confounding factors of seroconversion after SARS-COV2 vaccination into account. Results are reported as odds ratios (OR) and 95% confidence intervals (95% CI). We performed a complete case analysis as covariate information was missing in one patient only for the multivariate model. The study was approved by the Ethics Committee of the Johannes Kepler University Linz (ID: 1100/2021). Patients provided written informed consent. Patient demographics and additional analyses are shown in the Supplementary Material.

No abstract

No abstract