Currently, there is no recommendation for a routine booster dose of vaccine after receiving three doses at birth. This study will provide valuable information regarding the need for and response to an additional dose (booster dose) of hepatitis B vaccine among children entering primary school or adolescence. If evidence of waning immune memory (as measured by a delayed or diminished response to the additional dose of vaccine) is found, these two age groups would be the most easily accessible for routine delivery of a booster dose.