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From the literature.

In 1981–1982, a total of 1578 Alaska Natives who were serologically negative for hepatitis B infection received 3 doses of the plasma-derived hepatitis B vaccine, Heptavax (Merck). Six months after receipt of the last dose, 94% had a serum level of antibody to hepatitis B surface antigen (anti-HBs) of 10 mIU/mL, indicating an adequate immunologic response to the vaccine. Evaluation of 841 vaccine recipients (53%) who were available for follow-up testing 15 years later found that the geometric mean concentration of antiHBs had decreased during this time from 822 to 27 IU/L, and 84% of those tested at 15 years had positive anti-HBs levels ( 2 mIU/mL). After adjustment, the lowest anti-HBs levels at 15 years were associated with having been vaccinated at age 6 months to 4 years. Sixty-two participants (5.4%) who had not received additional doses of vaccine were found to have a booster response (defined as a 2-fold increase in anti-HBs level) during the period of observation, indicating presumed natural exposure to hepatitis B virus (HBV) in a protected individual. True breakthrough infections, all of which were asymptomatic, were detected in 16 subjects (12 with definite and 4 with possible infections), for an incidence of 1.26 cases per 1000 person-years. Breakthrough infection was more common in vaccine nonresponders than in those who had responded. Only 6 of the 12 persons with definite breakthrough infection had detectable HBV DNA in serum. Two of these 6 were infected with wild-type virus alone, whereas, in the other 4, infection was caused by variant virus with surface glycoprotein mutations, and there was coinfection with wild-type virus in 3 of the 4. This study demonstrates that HBV vaccination provides excellent protection for at least 15 years. However, the more rapid decrease in antibody levels among subjects vaccinated at ages 6 months to 4 years raises the possibility of a lack of efficacy at a time when the possibility of sexual exposure to the virus reaches its peak. This may be an alarmist view, however, because immunologic memory may persist well beyond the period of production of detectable antibody levels. Only additional monitoring of cohorts such as this one for the development of breakthrough infections will provide us with the data required to determine whether booster vaccination is warranted in some groups at some time.