Efficacy of HBV booster dose administration in Italian medical students in relation to health determinants.

We evaluated the efficacy of a booster dose of HBV in Italian medical students. We conducted a prospective observational study in students who had received a full course of anti-HBV vaccination for at least 15 y. Those with an anti-HBs titer <10 mIU/mL were offered a booster dose of the HBV vaccine and the antibody titer was reevaluated after 1 month. The participants were classified into three categories: with anti-HBs titer >100 mIU/mL, between 10 and 100 mIU/mL and <10 mIU/mL. The study population was n. 625 medical student and 355 (56.8%) with anti HBs titer <10 mIU/mL were offered a booster dose. A total of 166 of them received the booster dose and 92.77% (38 + 116/166) achieved an anti-HBs titer ≥10 mIU/mL. The post-booster anti-HBs titer response was higher, i.e. >100 mIU/mL, in subjects who had a pre-booster anti-HBs titer between 1.00 and 9.99 mIU/mL (84.38%, 81/96), compared to those with titer <1 mIU/mL (50.00%, 35/70). Subjects with a titer <1.00 mIU/mL at enrollment showed no anamnestic response (post-booster anti-HBs <10 mIU/mL, RRR 0.23, 95% CI 0.06-0.84) and to a low anamnestic response (post-booster anti-HBs 10-100 mIU/mL, RRR 0.16, 95% CI 0.07-0.38). Physical activity was linked to a better antibody response to vaccination (post-booster anti-HBs 10-100 mIU/mL: RRR 2.39, 95% CI 1.05-5.59). Immune protection following primary vaccination against HBV tends to wane over time. Booster dose induces anamnestic responses, especially in individuals who maintain titer HBsAg >1 mIU/mL and do physical activity.