Poliomyelitis is a contagious infectious disease that is caused by three types of poliovirus. The viruses cause damage and destruction of cells in the nervous system. Paralysis can result in about 2% of those who contract the disease, which is called polio. Most people who contract polio either have mild symptoms or no symptoms at all.

Poliomyelitis has been part of human history for millennia. An Egyptian stone engraving depicting the debilitating effects of poliomyelitis dates from over 3,000 years ago. In that time, the occurrence of polio was rare, as sanitation was poor. The close proximity between people and raw sewage bestowed protective immunity against the polioviruses, which reside in the feces. As sewage treatment became better and indoor plumbing became widespread in the twentieth century, exposure to the virus became less and the protective immunity was less likely to develop in children. By the...