Risk factors for paralysis No one knows why only a small percentage of infections lead to paralysis. Several key risk factors have been identified as increasing the likelihood of paralysis in a person infected with polio. These include: immune deficiency pregnancy removal of the tonsils (tonsillectomy) intramuscular injections, e.g. medications strenuous exercise injury - See more at: http://www.polioeradication.org/Polioandprevention.aspx#sthash.vykFd76Q.dpuf