Anti-SARS-CoV-2 Spike Antibody Response to Seven Doses of BNT162b2 mRNA COVID-19 Vaccine and Associated Factors in Hemodialysis Patients

Background: We evaluated the anti-SARS-CoV-2 spike antibody response following seven doses of the BNT162b2 messenger RNA COVID-19 vaccine in patients undergoing hemodialysis and investigated factors associated with antibody levels after the fifth, sixth, and seventh doses. Methods: Forty patients were recruited in the analysis of this single-center, prospective, longitudinal study. Changes in anti-SARS-CoV-2 spike antibody levels between the second and seventh doses were evaluated. Factors independently associated with the antibody levels after the fifth, sixth, and seventh doses were determined by multiple linear regression analyses. Results: The antibody level was significantly higher 4 weeks after the third dose than 4 weeks after the second dose (17,000 [interquartile range (IQR), 9916–30,500] vs. 2372 [IQR, 896–4206] AU/mL, p < 0.001). The level was also significantly higher 4 weeks after the fourth dose than 4 weeks after the third dose (27,000 [IQR, 10,453–46,500] vs. 17,000 [IQR, 9916–30,500] AU/mL, p < 0.05). However, the levels 4 weeks after the fifth, sixth, and seventh doses were not significantly different from the level 4 weeks after the fourth dose. The antibody level 1 week before vaccination was correlated with the antibody level 4 weeks after vaccination at the fifth dose (standard coefficient [β] = 0.736, p < 0.001), sixth dose (β = 0.601, p < 0.001), and seventh dose (β = 0.717, p < 0.001). Conclusions: The antibody level increased between the second and fourth doses and then plateaued through the seventh doses in hemodialysis patients. The pre-vaccination antibody level was associated with the post-vaccination antibody level at the fifth, sixth, and seventh doses in this population.