Abstract
BACKGROUND: Hepatitis A remains a public health concern, particularly in areas with suboptimal sanitation. Introduced in Turkey's immunization schedule in 2011, the vaccine has improved immunity; however, gaps persist, especially in older, unvaccinated children. This study examines the seropositivity rates and antibody levels in children across different vaccination statuses and age groups, and to identify gaps in immunity, particularly among children those born before the introduction of the hepatitis A vaccine in Turkey. METHODS: Data from 9,858 patients, collected between August 2019 and March 2024, were analyzed to evaluate the immunological response to the vaccine. Patients were categorized into four groups based on vaccination status: under-vaccinated (children 6-18 months old), single-dose vaccinated (children 18-24 months old), fully vaccinated (children over 24 months old born after March 1, 2011), and unvaccinated (born before March 1, 2011, when routine hepatitis A vaccination began). Seropositivity rates and antibody levels were measured and statistically analyzed. RESULTS: In this study, a total of 9,858 pediatric patients were assessed, with 1.1% under-vaccinated, 3.4% single-dose vaccinated, 60.5% fully vaccinated, and 35% unvaccinated. Seropositivity rates reached 93% in the fully vaccinated group, compared to 83% in the single-dose group and 63% in the unvaccinated group. Antibody titers were significantly higher in the fully vaccinated group, with statistically significant differences in seropositivity between this group and the unvaccinated group (p < 0.001). Additionally, a notable decrease in antibody levels was observed in the unvaccinated group as age increased (r = -0.365, p < 0.001). CONCLUSION: These findings underscore the critical need for targeted interventions to close vaccination gaps, especially among older, unvaccinated children who exhibit lower immunity levels. These insights are crucial for enhancing vaccination outreach and improving public health measures against hepatitis A.