Papers

Observational study of vaccine efficacy 14 years after trial of hepatitis B vaccination in Gambian children

Hilton Whittle, deputy director, ^a Shabbar Jaffar, senior lecturer, ^b Michael Wansbrough, MSc student, ^b Maimuna Mendy, senior scientific officer, ^a Uga Dumpis, visiting research fellow, Riga University, ^a Andrew Collinson, clinical scientist, ^a Andrew Hall, professor. ^b

^a Medical Research Council Laboratories, PO Box 273, Banjul, Gambia, ^b London School of Hygiene and Tropical Medicine, London WC1E 7HT

Correspondence to: H Whittle hwhittle{at}mrc.gm

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.

What is already known on this topic An expert panel has declared that booster immunisations are not needed for lifelong immunity to hepatitis B The evidence for maintenance of immunity in teenagers after vaccination in infancy is slender The risk of hepatitis B virus infection is increased by sexual exposure What this study adds Teenagers vaccinated in infancy have low concentrations of antibody to hepatitis B surface antigen Even though breakthrough infections are common at this age, protection against chronic infections with hepatitis B virus may be maintained