Seroepidemiological study of hepatitis B virus markers in Japan

In Japan, since 1986, selective vaccination has been implemented as a hepatitis B prevention strategy. The target of vaccination is the infant born to a hepatitis B surface antigen (HBsAg)-positive mother. The current Japanese hepatitis B prevention strategy focuses on reducing the number of HBV carriers but overlooks the risk to susceptible populations. We conducted a nationwide HBV seroepidemiological study to explore the next hepatitis B control strategy.

We used sera derived from healthy individuals collected nationwide from 2005 through 2011 to investigate the HBsAg seroprevalence among children aged 4-9 years and 10-15 years (3000 samples) and hepatitis B core antibody (HBcAb) seroprevalence among people 10-39 years of age (600 samples).

Among sera from 3000 children, 5 (0.17%) specimens were HBsAg-positive. There was no significant difference in HBsAg prevalence between age groups. Among 600 samples, 15 (2.5%) were HBcAb-positive. Out of 15 samples, 4 were from teenagers. Both HBsAg- and HBcAb-positive sera were found mainly in the Southern area of Japan.

The prevalence of HBsAg among children was 0.17% in the present study. This is higher than the prevalence reported in previous studies performed in the local area or in blood donors. The prevalence of HBcAb is also higher than we estimated. One of the reasons for this discrepancy from previous studies may be due to the small sample size and the impact of HBV high-endemic areas included in the present nationwide study. Nevertheless, our findings revealed that the opportunities for acquiring HBV infection in the susceptible population were more frequent than we thought, especially in some localities. Hepatitis B vaccination should be introduced into the routine child immunization program for susceptible populations, and the selective vaccination program should be continued for high-risk children.