Orlando Mayorga1, Silja Bühler2, Veronika K Jaeger3, Seraina Bally4,5, Christoph Hatz2,4,5, Gert Frösner6, Ulrike Protzer6, Pierre Van Damme7, Matthias Egger8, Christian Herzog4,5,8. 1. Department of Microbiology & Parasitology, Faculty of Medical Sciences, National Autonomous University, León, Nicaragua. 2. Epidemiology, Biostatistics and Prevention Institute, University of Zürich. 3. Department of Rheumatology, Basel University Hospital. 4. Medical Department, Swiss Tropical and Public Health Institute. 5. University of Basel, Switzerland. 6. Institute of Virology, Technical University of Munich/Helmholtz Zentrum München, Germany. 7. Centre for the Evaluation of Vaccination, Vaccine & Infectious Disease Institute, University of Antwerp, Belgium. 8. Institute of Social and Preventive Medicine, University of Bern, Switzerland.
Abstract
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.
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.