Since the introduction of vaccines against polio in the mid 1950s (Inactivated polio vaccine (IPV)) and the earl 1960s (Oral polio vaccine (OPV)), the control of polio has been successful. However, vaccine associated paralytic disease, which is caused by reversion of OPV, remains an unsolved issue in the present. Even though OPV has ability to induce a high level of intestinal immunity, it may ...