Polio, also known as poliomyelitis, is a highly infectious viral disease that can cause paralysis. Most of the world's countries are free from polio, although small numbers of cases are still reported in Afghanistan and Pakistan. In particular, it is found in areas where water treatment and sanitation facilities are not properly maintained or are nonexistent.
Although children under 5 years of age make up more than half of all cases, polio can affect people of any age.
The World Health Organization is at the heart of a plan to help make the world free from the disease. Since there is no animal infection or reservoir of the virus, the complete removal of the disease from the human population through vaccination is possible. The number of polio-endemic countries in 1988 was over 125; in early 2015, this number had been reduced to just 2, and the number of reported cases decreased from an estimated 350,000 in 1988 to 33 in 2018.