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.

Conclusion: 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.

Keywords: antibody persistence; hepatitis A vaccine; immunization programs; single dose.

Figure 1

Subject disposition. Notes: ¹Participants received one dose of HAV vaccine between June and December 2007; ²2-year anniversary of HAV vaccination; ³3-year anniversary of HAV vaccination; ⁴participants given one HAV vaccine dose before inclusion (Group A), participants given two doses before inclusion (Group B), participants given one dose before inclusion and a second dose during the study (Group C). Abbreviation: HAV, hepatitis A virus.

Figure 2

Anti-HAV geometric mean concentrations at years 1, 2, and 3 after primary vaccination. Notes: Group A, participants given one HAV vaccine dose before inclusion (n = 365); Group B, participants given two doses before inclusion (n = 94); Group C, participants given one dose before inclusion and a second dose during the study (n = 6). Abbreviation: HAV, hepatitis A virus.