Chronic and occult hepatitis B virus infections in the vaccinated Chinese population
In China, the prevalence of chronic hepatitis B virus (HBV) carriers declined from 9.5% to 7.2% in general population aged 1–59 years between 1992 when universal infant vaccination program was implemented nationwide and 2006. Approximately 75% to 90% reduction in hepatitis B surface antigen (HBsAg)-positivity was achieved in children, the HBsAg prevalence being reduced to 3% or less than 1% in children aged 5–14 years or <5 years, respectively. However, the non-responders with anti-HBs <10 IU/L and those with anti-HBs declining below the 100 IU/L protective level remain susceptible to breakthrough or occult HBV infections (OBI). Approximately 3–4% of HBV DNA carriers among the vaccinated population aged between 18 and 25 years, are HBV infected either vertically or horizontally from mothers, family contacts or sexual partners with high HBV viral load. The immunoprophylaxis efficacy of hepatitis B vaccine produced from an HBV genotype A2 strain may not be fully protective from HBV infection of genotype non-A2 strains, for instance, against HBV genotype B and C strains. An HBV vaccine boost between age 15 and 17 years might prevent asymptomatic infections acquired through sexual activity or other routes. Boosting at age 18–24 might induce an anamnestic response providing >100 IU/L of sero-protective anti-HBs level in college students. The implementation of a systematic hepatitis B boosting vaccination program for non- and low-responder children and adolescents at age 15–17 is suggested in China. Such strategy might be cost-saving and a significant health benefit for the Chinese population.