 It is estimated that 80–86 percent of individuals in a population must be immune to polio for the susceptible individuals to be protected by herd immunity.If routine immunization were stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.While vaccination has played an instrumental role in the reduction of polio cases worldwide, the use of attenuated virus in the oral vaccine carries with it an inherent risk.