Changes of Anti-Hbs Levels among Unboosted Young adults After Infantile Hepatitis B Vaccination: A Prospective Cohort Study

The duration of protection from infantile hepatitis B vaccination in adulthood, despite loss of antibody against hepatitis B surface antigen (anti-HBs), remains uncertain. In the present study, we longitudinally assessed changes in anti-HBs levels and protection among unboosted young adult vaccines. A total of 179 vaccinees completed the 1st and 2nd follow-ups were included. The mean duration between the 1st and 2nd follow-ups was 28.6±7.2 (19-44) months. The mean age of vaccinees was 20.3±2 years at the 1st follow-up. There were 64 (35.8%) females and 115 (64.2%) males. 11% of unboosted adults with baseline anti-HBs levels < 10 mIU/mL had increased levels (≥ 10 mIU/mL) after 2.3 years. In addition, 20% of vaccinees with anti-HBs ≥ 10 mIU/mL lost protective anti-HBs levels after 2.3 years. The anti-HBs level at the 1st follow-up was identified as an independent predictor of protective immune status at 2.3 years after follow-up. Breakthrough HBV infection was not detected among vaccinees with low or undetectable anti-HBs levels. In conclusion, these results demonstrate dynamic changes in anti-HBs and long-lasting protection from infantile hepatitis B vaccination among unboosted young adults. In addition, it emphasizes the strong predictive value of anti-HBs level in determining long-term seroprotection.