 For participants the study will consist of two visits at a four week intervalvisit 1 and visit 2. If the parentsguardians then sign the consent form a medical and immunisation history will be taken and a medical examination will be undertaken if indicated. If no exclusion criteria are identified, the child will be enrolled in the study. A 6ml blood sample will be taken from the child and single booster dose of Hepatitis B vaccine will be administered. 