LAUSR

INTRODUCTION The antibody response to SARS-CoV-2 vaccine in haemodialysis (HD) patients is diminished compared to healthy subjects. The aim of this study was to compare the presence of reactive SARS-CoV-2 antibodies in patients with high-flux HD and on-line haemodiafiltration (HDF) three and 6 months after the second dose of SARS-CoV-2 vaccine since previous studies indicate that a sustained antibody response correlates with protection from disease. METHODS We included 216 HD patients of which 157 had on-line HDF and 59 high-flux HD and 46 health care workers as controls and studied the presence of reactive anti-spike IgG antibodies three and 6 months after the second dose of SARS-CoV-2 vaccine. Clinical features between the patient groups were similar, but patients with on-line HDF had significantly higher Kt/V. RESULTS The percentage of participants with reactive antibodies was significantly lower in patients compared to controls, both three and 6 months after the second dose of vaccine. Furthermore, the proportion of patients with reactive anti-spike IgG ≥1.0 6 months after the second dose of vaccine was significantly higher in patients with on-line HDF compared to in patients with high-flux HD. In logistic regression analyses adjusted for several clinical features, the variables associated with presence of reactive anti-spike IgG at 3 months after the second dose of vaccine were lower age, HDF treatment, not being obese and not having a previous solid organ transplant. The two variables with the strongest influence on the presence of reactive anti-spike IgG levels 6 months after the second dose of vaccine were treatment with on-line HDF and not having immunosuppressive therapy. CONCLUSION This is the first study to show that on-line HDF preserves the antibody response better than high-flux HD after vaccination with SARS-CoV-2 vaccine. Treatment strategies that sustain the vaccine response are essential to apply in this vulnerable group of patients.