Polio is an infection of the spinal cord and brain, which can result in permanent muscular paralysis and death. Killed Polio virus vaccine (IPV) is given at 2 and 4 months. Boosters of this vaccine are given at fifteen months and four to five years of age. Polio vaccine used to be given by mouth (live, or Sabin vaccine – OPV) but is now only given by injection (killed, or Salk vaccine – IPV) and has no immediate side effects. It does not cause irritability or fussiness.