Low prevalence of hepatitis B vaccine escape mutants among individuals born after the initiation of a nationwide vaccination program in Iran

A nationwide hepatitis B virus (HBV) vaccination program for neonates was launched in Iran in 1993. Despite the success of this program, concern about its long-term success still remains, because breakthrough infections due to emergence of surface mutants have been reported in immunized children. We aimed to evaluate the seroprevalence of HBV and vaccine escape mutants among individuals born after the initiation of the nationwide vaccination program in Iran. This study included 1115 participants younger than 23 years old, with 223 in each age cohort. The presence of HBsAg, anti-HBs and anti-HBc was evaluated using an ELISA kit. HBV-DNA levels were measured in anti-HBc and/or HBsAg-positive subjects. PCR products were sequenced and mutations were identified. The overall HBsAg prevalence was 0.27 %. Anti-HBs and anti-HBc positive rates were 48 % and 0.18 %, respectively. Two individuals were positive for anti-HBc, one of whom was also positive for HBsAg, and the other was positive for anti-HBc only. HBV DNA was detected in three out of four anti-HBc-and /or HBsAg-positive subjects. An I195M mutation within the S gene was detected in two of the three HBV-DNA-positive cases. A very low prevalence of HBsAg and isolated anti-HBc were found in this study. The I195M mutation found in the surface gene could have been induced by immune pressure. Although the number of ‘‘vaccine escape’’ mutants found in this cohort was low, ongoing surveillance of breakthrough infections and escape mutants is still needed.