Post-polio syndrome occurs in approximately 25–50% of people who survive a poliomyelitis infection.^[1] On average, it occurs 30–35 years afterwards; however, delays of between 8–71 years have been recorded.^[2][3] The disease occurs sooner in persons with more severe initial infection.^[3] Other factors that increase the risk of postpolio syndrome include increasing length of time since acute poliovirus infection, presence of permanent residual impairment after recovery from the acute illness,^[2][3] and female sex.^[4]

Post-polio syndrome is documented to occur in cases of nonparalytic polio (NPP). One review states late-onset weakness and fatigue occurs in 14% to 42% of NPP patients.^[5]