INCREASES IN LEVELS OF ANTIBODY TO HEPATITIS-B SURFACE-ANTIGEN IN AN IMMUNIZED POPULATION

Hepatitis B vaccine is effective in preventing infection with hepatiti s B virus (HBV), but its duration of protection is unknown. To examine the effect of exposure to HBV on an immunized population, data were a nalyzed from a cohort of Alaska Natives who were immunized and then fo llowed up annually for 10 years. A boost in antibody to hepatitis B su rface antigen (anti-HBs) was defined as a fourfold rise in levels to g reater than or equal to 20 mIU/mL that was not accompanied by the pres ence of antibody to hepatitis B core antigen or attributable to interi m vaccination. During 10 years of follow-up, 8.2% of 1,595 vaccinees h ad boosts in anti-HBs. Persons with boosts did not differ significantl y from those without boosts in terms of age, gender, village, initial level of anti-HBs, or level of anti-HBs before the boost. These result s underscore the continued exposure to HBV among vaccinees and the con tinued protection against disease that the vaccine provides.