Safety and Efficacy of a Third Dose of the BNT162b2 Vaccine in Liver‐Transplanted and Healthy Adolescents

Objectives: According to our previous study, the 2‐dose‐BNT162b2 vaccination is less effective against the Omicron variant. This study aimed to assess the safety and efficacy of a 3‐dose‐BNT162b2 vaccination in liver‐transplanted (LT) and healthy adolescents. Methods: LT and healthy adolescents who met the inclusion criteria received a third dose of the BNT162b2 vaccine (30 µg). Antireceptor‐binding domain immunoglobulin and T‐cell‐specific responses to severe acute respiratory syndrome coronavirus 2 spike peptides were assessed 3 months before the third dose (Visit −1) and 0 (Visit 0), 1 (Visit 1), and 2 months (Visit 2) after the third dose. Antinucleocapsid immunoglobulin and neutralizing antibodies were assessed at Visits 0 and 1. Adverse events (AEs) were monitored. Results: Eleven LT and 14 healthy adolescents aged 14.64 (13.2, 15.7) years (44.2% male) had antireceptor‐binding domain immunoglobulin geometric mean titers of 1412.47 (95% confidence interval [CI], 948.18–2041.11) and 1235.79 (95% CI, 901.07–1705.73) U/mL at Visit −1 but increased to 38 587.76 (95% CI, 24 628.03–60 460.18) and 29 222.38 (95% CI, 16 291.72–52 401.03) U/mL (P < 0.05) at Visit 1, respectively. This was consistent with neutralizing antibodies (42.29% and 95.37% vs 44.65% and 91.68%, P < 0.001) and interferon‐γ‐secreting cells in LT and healthy adolescents at Visit 0 versus Visit 1, respectively. For serious AEs, an LT girl with autoimmune overlap syndrome died 5 months postvaccination from acute liver failure. Conclusions: In both LT and healthy adolescents, humoral and cellular immune responses were high after the 3‐dose‐BNT162b2 vaccination. However, serious AEs were suspected in LT adolescents with autoimmune diseases.