Observational study of vaccine efficacy 14 years after trial of hepatitis B vaccination in Gambian children
Hilton Whittle, Shabbar Jaffar, Michael Wansbrough, Maimuna Mendy, Uga Dumpis, Andrew Collinson, and Andrew Hall
BMJ 2002; 325: 569.

Objective: To determine the duration of protection from hepatitis B vaccine given in infancy and early childhood.
Design: Cross sectional serological study of hepatitis B virus infection in children of various ages 14 years after the start of a trial of vaccination regimens.
Setting: Two villages in the Gambia.
Participants: Children and adolescents given hepatitis B vaccine in infancy or early childhood: 232 were aged 1-5 years, 225 aged 5-9 years, 220 aged 10-14 years, and 175 aged 15-19 years.
Main outcome measures: Vaccine efficacy against infection and against chronic infection in the different age groups.
Results: Vaccine efficacy against chronic carriage of hepatitis B virus was 94% (95% confidence interval 89% to 97%), which did not vary significantly between the age groups. Efficacy against infection was 80% (76% to 84%). This was significantly lower in the oldest age group (65%, 56 to 73). Of the uninfected participants in this age group, 36% had no detectable hepatitis B virus surface antibody. Time since vaccination and a low peak antibody response were the most powerful risk factors for breakthrough infection (P<0.001 in each case). Low peak antibody response was also a risk factor for chronic carriage (odds ratio 95, 19 to 466).
Conclusions: Children vaccinated in infancy are at increased risk of hepatitis B virus infection in the late teens. The risk of chronic carriage after sexual exposure needs further assessment to determine if booster vaccines are necessary