The success of this vaccination strategy is contingent on the vaccine being able to induce long-lasting protection. The duration of protection conferred by hepatitis B vaccination initiated at birth is not firmly established. Over 95% of vaccinees in clinical studies develop a response to the three-dose primary hepatitis B vaccination series, defined as the development of antibody to hepatitis B virus surface antigen (anti-HBs) to concentrations greater than10 milliInternational Units per milliliter (mIU/mL) in blood. Within 5-10 years after the primary series, anti-HBs concentrations decline and for many vaccinees, concentrations will fall below 10mIU/mL, or even below detectable levels.