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



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.



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.



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.
Department of Microbiology & Parasitology, Faculty of Medical Sciences, National Autonomous University, León, Nicaragua.
Orlando
O
Mayorga
Epidemiology, Biostatistics and Prevention Institute, University of Zürich.
Silja
S
Bühler
Department of Rheumatology, Basel University Hospital.
Veronika K
VK
Jaeger
Medical Department, Swiss Tropical and Public Health Institute.|University of Basel, Switzerland.
Seraina
S
Bally
Epidemiology, Biostatistics and Prevention Institute, University of Zürich.|Medical Department, Swiss Tropical and Public Health Institute.|University of Basel, Switzerland.
Christoph
C
Hatz
Institute of Virology, Technical University of Munich/Helmholtz Zentrum München, Germany.
Gert
G
Frösner
Institute of Virology, Technical University of Munich/Helmholtz Zentrum München, Germany.
Ulrike
U
Protzer
Centre for the Evaluation of Vaccination, Vaccine & Infectious Disease Institute, University of Antwerp, Belgium.
Pierre
P
Van Damme
Institute of Social and Preventive Medicine, University of Bern, Switzerland.
Matthias
M
Egger
Medical Department, Swiss Tropical and Public Health Institute.|University of Basel, Switzerland.|Institute of Social and Preventive Medicine, University of Bern, Switzerland.
Christian
C
Herzog
D002648:Child; D002675:Child, Preschool; D019353:Endemic Diseases; D005260:Female; D005500:Follow-Up Studies; D006506:Hepatitis A / Q000453:epidemiology / Q000517:prevention & control*; D022362:Hepatitis A Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D006801:Humans; D056724:Immunity, Humoral; D007115:Immunization Schedule; D007156:Immunologic Memory; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009527:Nicaragua / Q000453:epidemiology; D010865:Pilot Projects; D016896:Treatment Outcome
D022362:Hepatitis A Vaccines
booster interval; children; hepatitis A; hepatitis A vaccine; immune memory; long-term follow-up; protective effectiveness; single-dose vaccination