Single-dose universal Hepatitis A immunization in one year old children in Argentina: High prevalence of protective antibodies up to 9 years following vaccination
Background: Single-dose Hepatitis A Virus (HAV) vaccination was implemented in all Argentinean children aged 12 months in 2005. Previous studies demonstrated high prevalence of protective antibody response 4 years following single dose vaccination. This study assessed long term seroprotection against HAV after vaccination. Methods: Children who received one dose of HAV vaccine at 1 year of age at least six years before enrollment were included at five centers in Argentina between 2013 and 2014. Demographic and socioeconomic characteristics were collected through a questionnaire. Blood samples were tested for anti-HAV antibodies. Antibody values >=10 mIU/mL were considered seroprotective. Logistic regression analysis was done to evaluate association between demographic and socioeconomic variables and seroprotection. Results: 1088 children were included, with a median post-vaccination interval of 7.7 years (range 6.3-9.2 y). From these, 97.4% (95% CI: 96.3%-98.3%) had protective antibodies against HAV. No association between demographic or socioeconomic variables and seroprotection was found. Geometric mean concentration (GMC) of antibody levels against HAV was 170.5 mUI/mL (95% CI 163.2-178.2 mUI/mL). Conclusions: Single-dose universal hepatitis A immunization in one year old children resulted in sustained immunologic protection for up to 9 years in Argentina. These findings, along with the low current disease burden, confirm the success of the intervention.