Few diseases scared 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. Poliomyelitis (often just called polio now) is an acute paralytic disease. It’s an enterovirus, 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, causing paralysis and death. There are 3 wild types of polio virus (types 1-3), which are naturally-occurring and non-mutated strains. There were serious outbreaks in Europe and the United States in the early 20th century, compelling scientists to try and find a vaccine. Although polio has no cure, as you will read in this timeline, vaccines have successfully eradicated polio in the western hemisphere since 1994.