Few diseases scared frightened parents in the early-20th century more than polio. It often struck in the warmer summer months, sweeping through cities and towns in epidemics every few years. Polio (short for poliomyelitis) is an acute paralytic disease. It’s an enterovirus, meaning it is a ribonucleic acid (RNA) virus that enters the body through the gastrointestinal tract where it thrives, but it can move to the nervous system. It's transmitted through contact with people, by nasal and oral secretions, and by contact with contaminated feces. Polio virus enters the body through the mouth, multiplying along the way and especially in the digestive tract.

Polio has existed since ancient times and was documented in the written record in the 18th and 19th centuries. There are three wild types of polio virus (types 1-3), which are naturally-occurring and non-mutated strains.