Hepatitis B immunity and response to a booster dose of hepatitis B vaccine in Indigenous children who recieved hepatitis B vaccines in infancy

This study is checking whether Aboriginal and Torres Strait Islander adolescents who received hepatitis B vaccines as babies still have adequate protection against hepatitis B infection. These participants were originally enrolled in a study called the Aboriginal Birth Cohort (ABC). The study will measure their current antibody levels, and those with low immunity will be offered booster doses of the hepatitis B vaccine to restore their protection. You may be eligible if: - You are between 16 and 19 years old - You were originally enrolled in the Aboriginal Birth Cohort (ABC) study You may NOT be eligible if: - You were not enrolled in the original Aboriginal Birth Cohort study - You do not agree to having your hepatitis B antibody level tested at baseline - Booster vaccination is only available to participants whose antibody level is below 10 IU/mL Talk to your doctor about whether this trial might be right for you.