FURTHER OBSERVATIONS ON THE IMMUNE-RESPONSE TO RECOMBINANT HEPATITIS-B VACCINE AFTER ADMINISTRATION TO ABORIGINAL AND TORRES STRAIT ISLAND CHILDREN

Objective: To determine the prevalence of markers of hepatitis B virus (HBV) immunity and infection at 5 years of age in Aboriginal and Torr es Strait Island children who were fully vaccinated in infancy, and to examine the response to a booster dose of hepatitis B vaccine in thos e children who had no detectable immunity despite vaccination. Methodo logy: A cross-sectional study of serological markers to HBV in a sampl e of 239 Aboriginal and Torres Strait Island children, with a mean age of 5.7 years, who were fully vaccinated in infancy. The antibody resp onse to a booster dose of hepatitis B vaccine was determined in those children in the sample who had no markers of either immunity to HBV or infection with HBV. Results: Of the 239 children, 6% (95% CI 4-10%) h ad been infected and, of these, four were HBV surface antigen (HBsAg) positive. Of the remaining 224 children, only 41% (95% CI 35-48%) had evidence of immunity (i.e. an antibody to HBV surface antigen (anti-HB s) level of greater than or equal to 10 miu/mL) to HBV. Of the childre n with no detectable immunity (i.e. anti-HBs <10 miu/mL), 113 were fol lowed up after receiving a booster dose of hepatitis B vaccine. Of the se, 84% (95% CI 76-90%) had an anamnestic response (i.e. anti-HBs (10 miu/mL following the booster dose). Therefore 16% (95% CI 10-24%) stil l had no detectable immunity following the booster dose. Conclusions: This study provides further evidence that Aboriginal and Torres Strait Island children have a suboptimal response to recombinant hepatitis B vaccine. It also indicates that a considerable number of Aboriginal a nd Torres Strait Island children in the study age cohort have been exp osed to HBV. However, despite these concerns, this study and historica l data provide strong evidence that there has been a marked reduction in the prevalence of HBV infection and carriage in previously 'high ri sk' Aboriginal and Torres Strait Island children since the introductio n of hepatitis B vaccines. Aboriginal and Torres Strait Island childre n who have been fully vaccinated in infancy do not require a booster d ose of hepatitis B vaccine at school entry.