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.