Polio virus, illustration. Each virus particle is composed of a protein coat around a core containing RNA genetic material. This virus infects children and causes the disease poliomyelitis or infantile paralysis. Although it normally causes a mild illness, in some cases it causes damage to the nervous system, which can lead to paralysis or death. Vaccination, starting in the 1950s, has been effective in controlling the disease. It has now been eliminated from Europe.