title: Persistence of immunity from 1 year of age after one or two doses of hepatitis A vaccine given to children in Argentina.
abstract: BACKGROUND
  This study was done to determine the immunogenicity of a single dose of hepatitis A vaccine in children, providing needed clinical data on the flexibility of booster administration.
  
  
  METHODS
  Participants had received one dose of inactivated hepatitis A vaccine (Avaxim™ 80 U Pediatric) at 12-23 months of age or two doses of the same vaccine at 12 and 18 months of age prior to enrolment. Anti-hepatitis A antibody concentrations were measured at the first, second, and third year after vaccination. Suspected cases of hepatitis A in participant families were assessed and family socioeconomic data were collected.
  
  
  RESULTS
  A series of 546 participants were enrolled. Of 467 (85.5%) participants completing 3 years of follow-up, 365 had received a single vaccine dose and 94 had received two vaccine doses. Seropositivity (anti-HAV ≥ 10 mIU/mL) at 3 years was 99.7% after one dose and 100% after two doses. At one year, geometric mean concentrations were higher after two doses (1433.9 mIU/mL, 95% confidence interval [CI] 1108-1855) than one (209.7 mIU/mL, 95% CI 190.6-230.6). Geometric mean concentrations decreased in both groups during the study, but remained well above 10 mIU/mL through the third year. The geometric mean of 3-year to one-year anti-hepatitis A concentration ratios was 0.74 (95% CI 0.70-0.79) following one dose and 0.57 (95% CI 0.47-0.70) following two doses. The greatest decrease in geometric mean concentrations occurred during the third year, ie, 21.2% in the one-dose group and 40.8% in the two-dose group. Six participants became seronegative during follow-up and responded strongly to a booster dose. Anti-hepatitis A concentrations increased in 135 children (34.9%) in the second year and 50 (13.7%) in the third year; none lived in a family with a case of hepatitis A. Three confirmed cases of hepatitis A occurred in family members. Participants belonged to a middle-income, urban/suburban population with good sanitation facilities and water supplies.
  
  
  CONCLUSIONS
  A single dose of hepatitis A vaccine at 12-23 months of age resulted in hepatitis A seropositivity in all but one vaccinee after 3 years. Increased anti-hepatitis A serum concentrations suggested exposure to wild-type hepatitis A virus in this middle-class socioeconomic environment. Continuing surveillance is required to confirm the effectiveness of a single-dose hepatitis A vaccination; however, the results of the first three years are encouraging.
authors.affiliation: Programa de Lucha Contra las Hepatitis Virales, Ministerio de Salud/Hospital Central de Mendoza, Mendoza, Argentina.
authors.forename: Carlos
authors.initials: C
authors.lastname: Espul
authors.affiliation: Programa Provincial de Inmunizaciones, Ministerio de Salud, Mendoza, Argentina.
authors.forename: Laura
authors.initials: L
authors.lastname: Benedetti
authors.affiliation: Laboratorio de Virología, Hospital Central de Mendoza, Mendoza, Argentina.
authors.forename: Héctor
authors.initials: H
authors.lastname: Cuello
authors.affiliation: Sanofi Pasteur, Lyon, France.
authors.forename: Guy
authors.initials: G
authors.lastname: Houillon
authors.affiliation: Sanofi Pasteur, Lyon, France.
authors.forename: Anvar
authors.initials: A
authors.lastname: Rasuli
keywords: antibody persistence; hepatitis A vaccine; immunization programs; single dose