The post-booster anti-PT geometric mean concentration was 82.5 EL.U/ml (95% CI 67.0–101.6) in the 0.3 mg group 108.1 (95% CI 87.7–133.2) in the 0.133 mg group and 124.0 (95% CI 103.5–148.5) in the 0.5 mg group, reaching numerically higher GMC levels compared to the first booster dose in the 0.133 mg and 0.5 mg groups (Fig. 2).