In other countries, most hepatitis B infection takes place during adolescence, transmitted horizontally through direct contact such as sexual activity. If they had been inoculated against hepatitis B as babies, it would have been like giving birth control to an old woman: a superfluous action.
國外 B 肝感染多在青少年時期，經由性行為等親密接觸而「水平感染」，他們若在嬰兒身上施打 B 肝疫苗，彷彿是「要老太婆吃避孕藥」般，多此一舉。