Polio cases have dropped by more than 99 percent since 1988 thanks to vaccines, the World Health Organization reports, but endemics exist in three countries: Afghanistan, Nigeria and Pakistan. The poliovirus is highly contagious and can cause paralysis, breathing problems and death. WHO reports that from 2009 to 2010, spread of the virus resulted in 23 formerly polio-free countries becoming re-contaminated.
The disease, which may date back hundreds of years, is responsible for epidemics in the 19th and 20th centuries. The discovery of an injectable vaccine in 1955 (and an oral one in 1961) has nearly wiped out polio in developed countries. According to WHO, there were 1,352 reported cases worldwide in 2010.
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