Immunogenicity and safety of a third dose of anti‐SARS‐CoV ‐2 BNT16b2 vaccine in liver transplant recipients

Background & aims A strategy to improve the low rate of anti‐SARS‐CoV‐2 mRNA vaccine‐induced immunogenicity in liver transplant recipients (LTs) is urgently needed. Methods We analysed the rate of positive (≥0.8 U/ml) anti‐SARS‐CoV‐2 receptor domain‐binding protein (RBD) antibody response 2 months after a third dose of the BNT16b2 vaccine in 107 LTs who completed the second vaccine dose 7 months earlier. Results A positive anti‐SARS‐CoV‐2‐s‐RBD antibody response after the third vaccine dose was detected in 98 (91.6%) LTs compared to 82 (76.6%) after the second vaccine dose (p = .003). The median of anti‐SARS‐CoV‐2 RBD antibody titres increased from 22.9 U/ml 6 months after the second to 3500 U/ml 2 months after the third vaccine dose (p < .001). Fourteen (14.3%) responder patients presented antibody titres <100 U/ml, 57 (58.2%) between 100 and 9999 U/ml and 27 (27.6%) ≥10 000 U/ml. Seropositivity after the second dose was maintained after the third dose. Independent predictors of antibody response failure after the third vaccine dose were taking a higher daily dose of mycophenolate mofetil (MMF, p < .001) and had a lower (<60 ml/min/1.73 m2) estimated glomerular filtration rate (p = .007). Nine (9.1%) LTs experienced symptomatic SARS‐CoV‐2 infection after the third vaccine dose. Median antibody titres were not statistically different between infected and not infected LTs (1325 vs 3515 U/ml, p = .678). Conclusions The third dose of the BNT16b2 vaccine increased the number of LTs who developed a positive anti‐SARS‐CoV‐2 s‐RBD antibody response. A proportion of patients remained unresponsive, mainly for modifiable factors, such as the use of MMF or multiple immunosuppressants.