Sustained seropositivity up to eight years after two-dose inactivated hepatitis A vaccination in Turkish children: a retrospective observational study.

BACKGROUND

Türkiye introduced a two-dose inactivated hepatitis A vaccination program in 2012 as part of the national childhood immunization schedule. However, data on the long-term persistence of vaccine-induced immunity in Turkish children remain limited. This study aimed to evaluate the durability of anti-HAV IgG responses following routine childhood hepatitis A vaccination.

METHODS

A retrospective cross-sectional study was conducted including 551 children who completed the two-dose hepatitis A vaccination schedule and 481 age-matched unvaccinated children. Vaccination status and anti-HAV IgG antibody levels were obtained from electronic hospital records. Serological testing was performed using a chemiluminescence microparticle immunoassay. Anti-HAV IgG levels ≥ 1 mIU/mL were considered protective.

RESULTS

Anti-HAV IgG seropositivity was 97.8% among vaccinated children. Seropositivity rates remained high over time but showed a gradual decline from 99.4% in the first year to 90.0% in the eighth year after vaccination. Despite this decrease, the majority of vaccinated children remained seropositive throughout the follow-up period. In contrast, seropositivity was 38.7% in the unvaccinated group, reflecting natural exposure to hepatitis A virus in the population. Because of the retrospective cross-sectional design, longitudinal antibody changes, clinically confirmed hepatitis A cases, and possible silent HAV infections could not be systematically evaluated.

CONCLUSIONS

Our findings demonstrate that a two-dose inactivated hepatitis A vaccination schedule provides sustained serological protection for up to eight years in Turkish children. Although anti-HAV antibody levels gradually declined over time, seropositivity rates remained high throughout the study period, suggesting persistence of immunological protection. The maintenance of immune memory despite decreasing antibody concentrations may contribute to continued protection. Further long-term prospective studies evaluating both humoral and cellular immune responses are needed to better define the duration of protection and assess the potential need for booster vaccination.