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Poliomyelitis (polio) is a highly infectious disease caused by a virus that invades the nervous system. It was one of the most dreaded childhood diseases of the 20th Century in the United States. There were usually about 13,000 to 20,000 cases of paralytic polio reported each year in the US before the introduction of Salk inactivated polio vaccine (IPV) in 1955. In 1965, only 61 cases of paralytic polio were reported.
Up to 95% of persons infected with polio will have no symptoms. About four to eight percent of infected persons have minor symptoms such as fever, fatigue, nausea, headache, flu-like symptoms, stiffness in the neck and back, and pain in the limbs which often resolves completely. Fewer than one percent of polio cases result in permanent paralysis of the limbs (usually the legs). Of those paralyzed, 5-10% die when the paralysis strikes the respiratory muscles.
Contact with an infected person.
There are two types of vaccine that can prevent polio: inactivated polio vaccine (IPV) and oral polio vaccine (OPV). IPV has been used in the United States since 2000; however OPV is still used throughout much of the world.