Polio, short for poliomyelitis, or infantile paralysis, is an infectious disease caused by the poliovirus. In about 0.5 percent of cases, there is muscle weakness resulting in an inability to move. In those with muscle weakness, about 2 to 5 percent of children and 15 to 30 percent of adults die.

Poliovirus is usually spread from person to person through infected fecal matter entering the mouth. It may also be spread by food or water containing human feces and less commonly from infected saliva. Those who are infected may spread the disease for up to six weeks even if no symptoms are present. The disease is preventable with the polio vaccine; however, multiple doses are required for it to be effective.

In the early 20th century, polio was one of the most feared diseases in industrialized countries, paralysing hundreds of thousands of children every year. The first polio vaccine was developed in the 1950s by Jonas Salk. Soon after its introduction polio was brought under control and practically eliminated as a public health problem in these countries.

In 1988, when the Global Polio Eradication Initiative began, polio paralysed more than 1,000 children worldwide every day. Since then, more than 2.5 billion children have been immunized against polio thanks to the cooperation of more than 200 countries and 20 million volunteers.

Today, wild poliovirus circulates in only two countries, Pakistan and Afghanistan.

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