Single-Dose Hepatitis A Immunization: 7.5-Year Observational Pilot Study in Nicaraguan Children to Assess Protective Effectiveness and Humoral Immune Memory Response

J Infect Dis. 2016 Nov 15;214(10):1498-1506. doi: 10.1093/infdis/jiw411. Epub 2016 Sep 6.


Background: Universal 2-dose hepatitis A virus (HAV) vaccination of toddlers effectively controls hepatitis A. High vaccine costs, however, impede implementation in endemic countries. To test single-dose vaccination as a possible alternative, we initiated an observational, longitudinal study in Nicaragua, to assess protective effectiveness and-through challenge vaccination-humoral immune memory response.

Methods: After a 2003 serosurvey, 130 originally seronegative children received one dose of virosomal HAV vaccine in 2005, followed by yearly serological and clinical assessments until 2012. After 7.5 years, a vaccine booster was administered. Concurrent antibody screening of patients presenting with hepatitis symptoms documented persistent HAV circulation in the communities studied.

Results: Between serosurvey and vaccination, 25 children contracted hepatitis A subclinically (>8000 mIU/mL anti-HAV). In the remaining 105 children, immunization resulted in anti-HAV levels of 17-572 mIU/mL. Based on the ≥15% annual infection risk, an estimated 60% of children were exposed to HAV encounters during follow-up. No child presented with hepatitis symptoms. Serological breakthrough infection (7106 mIU/mL) was documented in 1 child, representing an estimated protective effectiveness of 98.3% (95% confidence interval, 87.9-99.8). Boosting elicited an average 29.7-fold increase of anti-HAV levels.

Conclusions: In children living in hyperendemic settings, a single dose of virosomal HAV vaccine is sufficient to activate immune memory and may provide long-term protection.

Keywords: booster interval; children; hepatitis A; hepatitis A vaccine; immune memory; long-term follow-up; protective effectiveness; single-dose vaccination.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Child
  • Child, Preschool
  • Endemic Diseases
  • Female
  • Follow-Up Studies
  • Hepatitis A / epidemiology
  • Hepatitis A / prevention & control*
  • Hepatitis A Vaccines / administration & dosage*
  • Hepatitis A Vaccines / immunology*
  • Humans
  • Immunity, Humoral*
  • Immunization Schedule*
  • Immunologic Memory*
  • Infant
  • Longitudinal Studies
  • Male
  • Nicaragua / epidemiology
  • Pilot Projects
  • Treatment Outcome


  • Hepatitis A Vaccines