he naturally occurring polio virus is known as 'wild virus'. It is the wild virus that causes paralytic polio in countries where the infection is endemic. There are 3 subtypes of polio virus.
Infection with wild poliovirus gives lifelong immunity, but only to the particular subtype involved (types 1, 2 or 3).
Polio associated with vaccines:
Vaccine-induced paralytic polio (VAPP):
Rarely, the live attenuated vaccine virus in the oral polio vaccine (OPV) can cause paralysis - either in the vaccinated child, or in a close contact. Immune deficiency of the recipient may contribute. This occurs in about 1 in 2.5 million doses of the vaccine.