Impact of recurrent epidemics of hepatitis a virus infection on population immunity levels: Bristol Bay, Alaska.

The dynamics of population-based immunity were examined by using serologic surveys of 7 villages in rural Alaska between 2 epidemics of hepatitis A virus (HAV) and after the second epidemic (1988-1990). Among persons aged 2-30 years, the overall age-adjusted prevalence of antibody to HAV (anti-HAV) was 51% in 1983 and 49% in 1993 (P=.506). In children aged <5 years, prevalence rates were 0% and 11% in 1983 and 1993, respectively. The prevalence of HAV infection increased with age in both surveys. When examined by 5-year birth cohorts, anti-HAV prevalence increased in children born between 1979 and 1983 (P<.001). Between the 2 survey periods, 43 clinical cases of HAV infection were reported in these villages; all occurred from 1988 to 1990. Despite high overall prevalence of immunity, transmission during epidemics was facilitated by children aged <15 years susceptible to HAV. Little transmission occurred between epidemics. Vaccination of children against HAV should prevent future epidemics.