AIM:To evaluate the impact of mass vaccination against the hepatitis B virus (HBV) in Egypt,and to search for vaccinee asymptomatic breakthrough HBV infection and its genotype.METHODS:Seven hundred serum samples from vaccinated children and adults (aged 2-47 years) were used for quantitative and qualitative detection of HBsAb by ELISA.Three hundred and sixty serum samples representing undetectable or low or high HBsAb were screened for markers of active HBV infection (HBsAg,HBcAb (IgG) and HBeAb by ELISA,plus HBsAg by AxSYM) and HBV-DNA genotyping by nested multiplex PCR and by DNA sequencing.RESULTS:It was found that 65% of children aged 2-4 years,and 20.5% aged 4-13 years,as well as 45% adults were good responders to HBV vaccination mounting protective level HBsAb.Poor responders were 28%,59.5% and 34%,and non-responders were 7%,20% and 21% respectively,in the three studied groups.Markers of asymptomatic HBV infections were HBsAg detected by ELISA in 2.5% vs 11.39% by AxSYM.Other markers were HBcAb (IgG) in 1.38%,HBeAb in 0.83%,and HBV-DNA in 7.8%.All had HBV genotype E infection.CONCLUSION:It is concluded that HBV vaccine is efficient in controlling HBV infection among children and adults.The vaccine breakthrough infection was by HBV genotype E.A booster dose of vaccine is recommended,probably four years after initial vaccination. AIM: To evaluate the impact of mass vaccination against the hepatitis B virus (HBV) in Egypt, and to search for vaccinee asymptomatic breakthrough breakthrough HBV infection and its genotype. METHODS: Seven hundred serum samples from vaccinated children and adults (aged 2-47 years ) were used for quantitative and qualitative detection of HBsAb by ELISA. Three hundred and sixty serum samples representing undetectable or low or high HBsAb were screened for markers of active HBV infection (HBsAg, HBcAb (IgG) and HBeAb by ELISA, plus HBsAg by AxSYM ) and HBV-DNA genotyping by nested multiplex PCR and by DNA sequencing .RESULTS: It was found that 65% of children aged 2-4 years, and 20.5% aged 4-13 years, as well as 45% adults were good responders to HBV vaccination mounted protective level HBsAb. Supplements were 28%, 59.5% and 34%, and non-responders were 7%, 20% and 21% respectively, in the three studied groups. Markers of asymptomatic HBV infections were HBsAg detected by ELISA in 2.5% vs 11.39% by AxSYM.Other mar It was confirmed that it was HBV vaccine that was efficient in controlling HBV infection among children and adults. vaccine breakthrough infection was by HBV genotype EA booster dose of vaccine is recommended, probably four years after initial vaccination.