Anti-spike antibody responses in hemodialyzed patients vaccinated with anti-COVID-19 BNT162B2 mRNA vaccine

Background: Patients under hemodialysis are at higher risk of developing severe complications upon SARS-CoV-2 infection and were prioritized in the Portuguese vaccination campaign. Methods: We performed a longitudinal analysis of antibody responses upon vaccination with BNT162b2 mRNA (Pfizer/BioNTech, Comirnaty) in a cohort of 156 hemodialyzed patients. Direct ELISA was used to quantify IgG, IgM and IgA anti-fulllength Spike antibody levels against calibrated sera from naturally infected patients at three points: day of the first vaccine dose (t0);3 weeks later (day of the second dose, t1), and 3 weeks after the second inoculation (t2) for 143/156 patients. Anti-n was also measured in t0 and patients anti-n positive were excluded. Results: We observed that 90.9% of the patients developed anti-spike IgG antibodies after the second vaccine dose (t2). Seroconversion was remarkably low at t1 after the first vaccine dose with only 29.4% of patients developing anti-spike IgG antibodies. In addition to positivity, the second vaccine dose markedly increased IgG antibody levels. IgA levels were also higher at t2 with 83.9% of the patients achieving positivity while IgM positivity only reached 29.4%. Age showed a significant negative effect on the humoral response at t2 for anti-Spike IgG and for IgM, particularly over 60 years. Further analysis revealed that nine patients under immunosuppression therapies showed significantly lower humoral response along the vaccine schedule (p=0.005 at t1;p=0.008 at t2). Interestingly, the inability to develop anti-HBs antibodies upon hepatitis B vaccination frequently found in hemodialyzed patients was not correlated with lack of responsiveness to SARS-CoV-2 vaccination. Conclusions: The large majority hemodialyzed patients showed a significant humoral response to BNT162b2 mRNA vaccination, but a sizable proportion of patients showed low antibody levels when compared to responses in the general population (medRxiv 2021.03.19.21253680).