Prevalence of chronic HBV infection in The Gambia, by year of birth: born before routine infant HBV vaccination; vaccinees and controls born during the Gambia Hepatitis Intervention Study (GHIS) in 1986–90; born since nationwide infant HBV vaccination. Key: Number positive for HBV surface antigen (HBsAg)/number surveyed, % positive, and range of ages in years (y) when surveyed. Open circles = unvaccinated, closed circles = vaccinated in infancy (or supposed to be, in the Gambian EPI). Keneba: Unvaccinated historical controls (one village, children surveyed in 1984 at ages 1–19 years). West Africa median: Median of survey-specific HBsAg prevalences in 83 population surveys of unvaccinated children or adults conducted between 1990–2009 in West Africa (Merrill & Hunter, 2011). GHIS: Vaccinees and concurrent controls in the Gambia Hepatitis Intervention Study of children born in 1986–90, and surveyed for the present study in 2007–08, at ages 17–22 years, 0 · 8% vs 12 · 4% p < 0 · 00001. EPI: Population sample of children born since 1990 and surveyed for the present study in 2007–08 to assess the effectiveness of nationwide infant HBV vaccination (in the Gambian Expanded Programme on Immunisation), 1990–97 births 1 · 4% vs 1998–2007 births 0 · 3%, p < 0 · 00001.
Peto et al. BMC Infectious Diseases 2014 14:7 doi:10.1186/1471-2334-14-7