Persistence of antibodies to the surface antigen of the hepatitis B virus (anti-HBs) in children subjected to the Expanded Programme on Immunization (EPI), including hepatitis-B vaccine, in Thailand.

Will hepatitis-B vaccine administered at birth and at 2 and 6 months of age as an integral part of Thailands Expanded Programme on Immunization provide long-term protection? In an attempt to answer this question residents of five provinces (representing five distinct geographical areas of Thailand) who were aged 1-10 years and had received this course of vaccination were enrolled on a serological study. Each was tested with enzyme-linked immunosorbent assay for the surface antigen of hepatitis B (HBsAg) and for antibodies against this antigen (anti- HBs) or against the core antigen (anti-HBc). Over all age-groups the prevalences of HBsAg anti-HBs and anti-HBc were 0.67% 71.4% and 5.5% respectively. Although the prevalence of anti-HBs decreased with age it remained at 56-65% among those aged 6-10 years. Between 2% and 17% of the subjects aged 1-9 years had high titers of anti-HBs. Based on these results an additional booster still a controversial issue does not appear to be required in order to prevent infection with hepatitis B virus and thus permit the eventual eradication of chronic carriage and its fatal sequelae in Thailand. (authors)