Although there is good evidence that the immunologic memory for HBsAg exceeds the persistence of measurable antibodies, few studies have examined lasting protection (>10 years) against HBV infection in a low-risk population vaccinated at birth with recombinant vaccine.10 Most studies demonstrating long term protection from infection and persistent immune memory despite low anti-HBs concentrations have been performed among children living in areas where HBV infection is endemic, or whose mothers had chronic HBV infection (i.e., children at high risk of perinatal or childhood HBV infection). Studies conducted among Alaska Native children have demonstrated that "low-risk" children (i.e., infants who were born to HBsAg-negative mothers with no HBsAg-positive persons living in their households) also have concentrations of anti-HBs that fall below 10mIU/mL during later childhood. In a cohort of 36 children known to have responded to a recombinant vaccine series starting at birth, none retained levels of anti-HBs ≥ 10mIU/mL at 7.5 years of age. In addition, three of these children failed to exhibit an anamnestic response to a booster dose given at an average age of 7.5 years.