Smallpox
Smallpox is immunization's greatest success story to date, as this dreaded disease has been eradicated from the world. This disease was so prevalent in Europe in the 18th century that it was not uncommon for royalty who survived the disease to direct the artists that they commissioned to paint out or hide the permanent scarring that resulted from the disease in their royal portraits.
Historically up to 30 percent of those infected died from the disease. In the early 20th century, tens of thousands of smallpox cases were reported in the U.S. each year and it is estimated that smallpox was responsible for 300-500 million deaths worldwide. As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that 2 million died in that year.
The last case of smallpox in the world occurred in Somalia in 1977. In 1980, scientists officially declared that vaccines had been successful at eradicating smallpox worldwide.