Vaccine effectiveness of routine infant hepatitis B vaccination/hepatitis B vaccine impact under immunisation programme

We will check how well the hepatitis B vaccine is working by taking small blood samples from 7,700 people aged from 1 to 21 across the country. By comparing vaccinated people against unvaccinated we will see if the protection against infections with hepatitis B that was seen in earlier studies continues into adulthood. We need to do this as liver disease (especially liver cancer) caused by Hepatitis B is a major killer in The Gambia and as the vaccine was only introduced 21 years ago we do not yet know if the vaccinations given in childhood are going to prevent infections and disease in adults.

We propose to study the effectiveness of Hepatitis B (HBV) vaccination in infancy against chronic active hepatitis in early adulthood. This will provide new evidence to determine if there is continued protection against HBV carriage and disease after such a long period of time and whether it continues despite the onset of sexual activity. Additionally we will screen those born since the introduction of HBV vaccination into the Expanded Programme of Immunisation (EPI) to further measure the impact of routine vaccination, specifically: what level of carriage is present at different ages; how these appear to be acquired; if rates follow a trend over time; and if there has been a shift in the viral genotype. Approximately 3,200 17-21 year olds from the Gambia Hepatitis Intervention Study (GHIS) will have blood samples taken and 4,500 under 17s who were born since the end of the GHIS will be screened for HBV. This information will inform decisions on the value of a booster dose of vaccine in teenagers, whether there is perinatal transmission that can be averted by giving a first dose of the vaccine on the day of birth, and will describe the performance of the EPI in real life conditions. The existing GHIS, and the following early adoption of the HBV vaccine nationwide, makes this a unique population in which to answer these questions and further define the effectiveness of the HBV vaccine. The large number of blood samples collected will also allow for the genetic testing of host and viruses.