Hepatitis a seroprevalence among young adults: Effects of ACIP immunization recommendations

Purpose The seroprevalence of antibodies to hepatitis A increases significantly with age, but the effect of recent hepatitis A immunization practices on seroprevalence is unknown. As part of a larger study of the patterns of hepatitis A seroprevalence among U.S. military recruits, we examined the age-specific rate of hepatitis A seroprevalence in young adults to determine the effect of the 2001 Advisory Committee on Immunization Practices (ACIP) regional adolescent catch-up immunization recommendations in this potentially immunized cohort. Methods A regionally-stratified random sample of n = 1,679 stored frozen serum specimens obtained in 2004 from U.S. military recruits aged 18–23 and born in the contiguous United States was tested for the presence of total anti-HAV (IgG + IgM) using the Diasorin ETI-AB-HAVK PLUS EIA assay. Crude rates of seroprevalence were calculated stratified by age group (18–19, 20–21, and 22–23) and ACIP region, defined by state of birth where catch-up immunization was recommended or was to be considered statewide (ACIP region 1), and where no statewide recommendation existed (ACIP region 2). Results Both ACIP regions demonstrated the highest rates of seroprevalence among the cohort aged 18–19 (ACIP region 1: 14.5%, 95% CI 11.2%–18.2% vs. ACIP region 2: 12.9%, 95% CI 10.3%–16.0%). Seroprevalence was lowest among the cohort aged 20–21 (ACIP region 1: 8.7%, 95% CI 5.1%–13.7% vs. ACIP region 2: 4.8%, 95% CI 2.6%–7.9%), and rose slightly in the cohort aged 22–23 in both regions. Age-specific rates of seroprevalence were significantly different between the 18–19 year old and 20–21 year old cohort in ACIP region 1 (p = 0.05 by χ2), and ACIP region 2 (p < 0.001 by χ2). Conclusions High rates of seroprevalence among the 18–19-year-old cohort are likely due to broad acceptance of adolescent hepatitis A immunization independent of regional ACIP recommendations. These results suggest catch-up adolescent immunization recommendations can produce a significant increase in age-specific immunity within a few years.