Antibody titer after administration of mRNA‐based vaccine against severe acute respiratory syndrome coronavirus 2 in liver transplant recipients

INTRODUCTION: The mRNA‐based vaccine was released as a COVID‐19 prophylactic; however, its efficacy in organ transplant recipients is unknown. This study aimed to clarify this in liver transplant recipients. METHODS: Herein, liver transplant recipients from two hospitals who received vaccines were included. Immunoglobulin‐G antibodies against the spike and nucleocapsid proteins were measured chronologically after the second, third, and fourth vaccine doses. RESULTS: Antibody levels in 125 liver transplant recipients and 20 healthy volunteers were analyzed. The median age at transplant was 35 (interquartile range 1, 53) years, and the period between transplant and the first dose was 15.2 ± 7.7 years. After the second and third doses, 89.1% and 100% of recipients displayed a positive humoral response, respectively. Anti‐spike antibodies after the second dose were significantly reduced at 3 and 6 months, compared to that at 1 month (26.0 [5.4, 59.5], 14.7 [6.5, 31.4] vs. 59.7 [18.3, 164.0] AU/mL, respectively, p < 0.0001). However, a booster vaccine significantly elevated anti‐spike antibodies in LT recipients (p < 0.0001) as well as in healthy controls (p < 0.0001). Additionally, the decay rate was comparable between the transplant recipients and controls (2.1 [0.8, 4.5] vs. 2.7 [1.1, 4.1] AU/mL/day, p = 0.9359). Only 4.0% of vaccinated transplant recipients were positive for anti‐nucleocapsid antibodies. CONCLUSION: Liver transplant recipients can acquire immunity similar to that of healthy people through vaccination against SARS‐CoV‐2. The antibody decay rate is the same, and booster vaccinations should be administered similarly to that in healthy individuals.