Background Haemodialysis (HD) patients are exposed to a high risk due to the SARS-CoV-2 pandemic. They are prone to acquiring the infection and are threatened by high mortality rates in case of infection. However, HD patients were not included in the efficacy trials of the SARS-CoV-2 vaccines. Such efficacy data would have been critical because HD patients show decreased responses against various other vaccines and this could translate to the SARS-CoV-2 vaccines as well. Methods We conducted a prospective cohort study that contained a group of 81 HD patients and 80 healthy controls. All of them had been vaccinated with the BioNTech/Pfizer mRNA vaccine (two doses, as per the manufacturer’s recommendation). The anti-SARS-CoV-2 S antibody response was measured for all participants 21 days after the second dose. The groups were compared using univariate quantile regressions and a multivariate analysis. The adverse events (AEs) of the vaccination were assessed via a questionnaire. Finally, a correlation between the HBs-Antibody response and the SARS-CoV-2 antibody response in the HD patients was established. Results The HD patients had significantly lower Anti-SARS-CoV-2 S antibody titres than the control patients 21 days after vaccination (median was 171 U/ml for dialysis patients and 2,500 U/ml for the controls). Further, the HD group presented less AEs than the control group. No correlation was found between the antibody response to previous Hepatitis B vaccination and that of the SARS-CoV-2 vaccine. Conclusions HD patients present highly diminished SARS-CoV-2 S antibody titres compared to a cohort of controls. Therefore, they could be much less protected by SARS-CoV-2 mRNA vaccinations than expected. Further studies to test alternative vaccination schemes should be considered.

1. Abstract 1.1 Background and Objectives Hemodialysis patients are prone to infection with SARS-COV2 and show a high probability of a severe course of disease and high mortality when infected. In many countries hemodialysis patients are prioritised in vaccination programs to protect this vulnerable community. However, no hemodialysis patients were included in efficacy trials of SARS CoV-2 vaccines and therefore efficacy and safety data for this patient group are lacking. These data would be critical, since hemodialysis patients showed decreased responses against various other vaccines and this could mean decreased response to SARS CoV-2 vaccines. 1.2 Design, setting, participants, and measurements We conducted a prospective cohort study consisting of a group of 81 hemodialysis patients and 80 healthy controls who were vaccinated with mRNA vaccine BNT162b2 (BionTech/Pfizer, 2 doses with an interval of 21 days). Anti-SARS-COV-2 S antibody response in all participants was measured 21 days after the second dose. The groups were compared with univariate quantile regressions and a multiple analysis. Adverse events (AEs) of the vaccination were assessed with a standardized questionnaire. We also performed a correlation of HBs-Antibody response with the SARS-COV-2 antibody response in the hemodialysis patients. 1.3 Results Dialysis patients had significantly lower Anti-SARS-COV-2 S antibody titres than healthy control patients 21 days after vaccination with BNT162b2 (median dialysis Patients 171 U/ml versus median controls 2500 U/ml). Age also had a significant but less pronounced influence on antibody titres. Dialysis patients showed less AEs than the control group. No significant correlation was found for Hepatitis B vaccine antibody response and SARS CoV-2 vaccine antibody response. 1.4 Conclusions Hemodialysis patients exhibit highly diminished SARS-COV-2 S antibody titres compared to a cohort of controls. Therefore these patients could be much less protected by SARS CoV-2 mRNA vaccination than expected. Alternative vaccination schemes must be considered and preventive measures must be maintained after vaccination.