Hidden burden of hepatitis B: occult HBV infection in vaccinated offspring of HBsAg-positive mothers in an endemic area.

Occult Hepatitis B virus infection (OBI) is prevalent among high-risk and immunized populations in regions with high endemicity. OBI could be reactivated and/or transmitted, making it a significant risk factor for liver disease progression, including cirrhosis and hepatocellular carcinoma. This cross-sectional study was conducted on vaccinated children born to HBsAg positive mothers in the Esfandiar region of Iran. Families with a member who tested positive for HBV were included in the study. Blood samples were collected, and serological assays were performed to detect anti-HBc, HBsAg, anti-HBs, and HBeAg. Molecular examinations, including DNA extraction, PCR assays and real-time PCR quantification, were performed to identify OBI. Subsequently, the amplified segment of the S gene underwent DNA sequencing for mutations analysis and HBV genotyping. In total, 100 children were examined: Serological assessments indicated positive results for anti-HBs, anti-HBc, and HBsAg in 43%, 5%, and 2% of cases, respectively. PCR assays revealed 6.1% prevalence of OBI (95% CI: 0.013-0.11). Phylogenetic analysis confirmed that all isolates belonged to HBV genotype D and sub-genotype D1. Mutational analysis identified immune escape mutations in the HBsAg protein, including T45N, P105A, and Q129H. The findings suggest a suboptimal protective efficacy of the HBV vaccine in this highly endemic region. The presence of OBI among vaccinated individuals highlights the potential for transmission through congenital and perinatal routes. Screening of mothers and women of childbearing age, administration of HBV immunoglobulin, and reinforcement of Hepatitis B vaccination programs are imperative in such regions.