Changes in antibody titer after four and five doses of the SARS-CoV-2 vaccine in Japanese post-kidney transplant patients

Introduction: Immunosuppressed patients exhibit low antibody acquisition rates following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. Kidney transplant recipients previously exhibited low antibody acquisition rates after two vaccine doses, which increased after the third dose. We evaluated antibody titers of Japanese post-kidney transplant patients after the fourth and fifth vaccinations. Methods: Antibody titers for SARS-CoV-2 spike protein were measured between 3 weeks and 3 months after the fourth or fifth vaccination. Results: Increased antibody acquisition rates were observed after the fourth (75.0% antibody-positive) and fifth (81.5% antibody-positive) vaccinations. The antibody-acquired group after the fourth vaccination exhibited a higher body mass index and estimated glomerular filtration rate (eGFR) than the non-acquired group. A higher eGFR was associated with antibody acquisition after the fifth vaccination. Conclusion: In Japanese post-kidney transplant patients, the antibody acquisition rate increased with each vaccine additional dose. Additional vaccinations are recommended to protect against SARS-CoV-2 infection.