Seven-year study of hepatitis B vaccine efficacy in infants from an endemic area (Senegal).

A booster dose of hepatitis B vaccine was given to 143 children in whom hepatitis B had not developed 1 year after initial vaccination. Over the next six years the incidence of hepatitis B in this group was 1.5% per year compared with 11.5% per year in a similar group of unvaccinated children. In the first 4 years the protective efficacy of the vaccine was 100%, but during the 5th and 6th years it fell to 67%. For maximum protection a second booster is needed, 5 years after the first.