Efficacy of hepatitis B vaccine in the Gambian expanded programme on immunisation.

ABSTRACT

PIP: As part of the Gambia Hepatitis Intervention Study, hepatitis B antigens and antibodies were assayed in 720 3-4 year old children who had received 4 doses of 10 mcg plasma-derived hepatitis B vaccine in infancy, the findings were compared with 816 controls. The cross sectional study took place from September, 1990, to July, 1991. Study subjects were tested for hepatitis B core antigen (HBcAg), as well as antigens and antibodies to hepatitis surface, e, and core protein, and those testing positive were tested a year later for HBsAg to determine chronic carrier status. Children negative for core antibody and surface antigen were considered uninfected; those positive for core antibody were considered infected; those positive for surface antigen 2 times 6 months apart were considered carriers. 4.6% of the vaccinated children were infected, and 0.6% were chronic carriers. 3 of these carriers had infected or carrier mothers, and 1 had only received 1 dose of vaccine. In the controls, there were 29% judged infected by anti-HBc, including 13% who were also positive for HBsAg. 86% of these were considered chronic carriers when tested a year later. Thus the vaccine was estimated to be 84% effective against infection and 94% effective against chronic carriage. The current Gambian vaccine consists of 2.5 mcg recombinant hepatitis B vaccine.