Poliomyelitis (polio) is a highly infectious disease caused by a virus that invades the nervous system and can cause severe paralysis. The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralyzed, 5-10% die when their breathing muscles become immobilized. Polio mainly affects children under five years of age. Naturally occurring polio was eliminated in the U.S. in 1979 and in the Western Hemisphere by 1991; however, worldwide efforts are continuing towards eradication of this contagious and devastating disease.