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Combined active-passive immunization against the hepatitis B virus: five-year follow-up of children born to hepatitis B surface antigen-positive mothers.

In order to evaluate the duration of "protective" concentrations (i.e. > or = 10 IU/liter) of antibody to hepatitis B surface antigen (HBsAg) in children vaccinated against hepatitis B in infancy, we followed 146 children born to HBsAg-positive mothers from birth to age 60 months. Children were seen at yearly intervals and tested for hepatitis B virus serologic markers. Of the children included in the study, 134 were protected against infection with development of antibody to HBsAg, 5 became HBsAg-positive and 6 failed to respond to the vaccine but did not become infected. Antibody concentrations fell progressively with the passage of time. The probability of maintaining a "protective" concentration of antibody in vaccine responders at age 60 months was 86% (95% confidence interval, 80 to 93%). Gender, ethnic origin, HBeAg status of the mother and immunization schedule had no influence on the rate of antibody loss. We conclude that in developed countries, the great majority of children vaccinated in infancy remain protected against infection at least until age 60 months. The need for booster doses of vaccine in this population will be determined by long term follow-up of immunized cohorts.