Response to tozinameran (BNT162b2) booster in twice-vaccinated kidney transplant and maintenance dialysis patients

Background Patients needing chronic RRT are at risk for severe COVID-19 and mount a lesser response to mRNA vaccination. We describe the impact of booster administration in these patients, amidst a third wave of infections and deaths. Methods In the setting of a prospective COVID-19-centred cohort study in dialysis and kidney transplant patients we examined humoral responses to booster vaccination, and subsequent infection risk. Results We quantified antibodies (DiaSorin) in 198 maintenance dialysis patients, 314 kidney transplant patients and 82 controls, without prior COVID-19 infection. Prior to boosting, 79% of controls, 35% of dialysis and 11% of transplant patients had levels [≥]59 AU/ml (putatively protective), while 8-54 days after a third injection, respective rates were 100%, 93% and 58%. Risk factors for antibodies <60 AU/ml despite booster injection were transplant vs dialysis, OR=18.4 (p<0.0001), transitioning from dialysis to transplantation or vice versa, OR=15.7 (p<0.01) and days post injection, OR=0.953 (p<0.05). Antibody step-up after the booster inversely correlated with the second dose step-up (r=-0.33, p<0.01). In this surge, 2 controls, 2 dialysis and 9 transplant patients had COVID-19. Antibody level [≥]59 AU/ml at any time point independently associated with reduced risk of infection during this surge, OR=0.264 (p=0.048). Conclusions We show that a third dose of tozinameran boosts antibody levels in patients receiving RRT, as it did in controls. Most patients have now reached antibody levels likely to protect from infection. Antibodies were higher after the third dose compared to previous peaks, which may hint that the latest immune response may be more robust and sustainable, even in immune-compromised patients. Kidney transplant recipients showed the most striking enhancement, exhibiting >5.5-fold increase in the percentage of patients with protective antibody levels. However, many transplant patients remain below threshold even after boost injection, necessitating further boosting strategies.