Background and Aims Despite the success of universal infant immunization initiated in Taiwan in 1984, occult hepatitis B virus infection (OBI) and circulating surface antigen mutants remain potential obstacles for eventual eradication of HBV infection. Methods From 3299 apparently healthy, neonatally–vaccinated subjects (<30 years of age ) enrolled during 2014 serosurvey, we recruited all HBsAg–positive (n = 17), all HBsAg–negative but anti‐HBc–positive (n = 132) and randomly selected HBsAg–negative and anti‐HBc–negative subjects (n = 411). These recruited subjects and 81 HBsAg–negative children with various forms of hepatitis and multiple transfusions were analysed for serum HBV DNA. Results In healthy, HBsAg–negative subjects, OBI frequency was higher in anti‐HBc–positive than anti‐HBc‐negative individuals (8/908.9% vs 8/3012.7%, P = 0.0192) aged <18‐years, but was not different between anti‐HBc–positive and anti‐HBc–negative individuals (0/110% vs 3/1102.7%, P > 0.05) aged 18 to 30 years. OBI occurred more frequently in children of HBsAg–positive mothers than in children of HBsAg–negative mothers (10/101 9.9% vs 1/75 1.3%, P = 0.025). The prevalence of surface ‘a’ determinant (aa110‐160) mutants was 13.3% (2/15) in OBI subjects compared to 36.4% (4/11) in HBsAg–positive subjects (P > 0.05). OBI was found in 30% (3/10) of serologic ‘non‐A to E’ viral hepatitis, 14.3% (3/21) of chronic hepatitis C and 2.0% (1/50) of multitransfused, thalassemic children. Conclusions In this highly immunized population, surface antigen mutant infection is uncommon and has low contribution to OBI development. HBsAg screening plus highly sensitive HBV DNA assays are needed for assurance of blood supply safety. Multiple transfusions from HBsAg–negative blood donors rarely result in persistent HBV infection. HBV might be related to some of serologic ‘non‐A to E’ viral hepatitis.