Smallpox was the first major disease to be eradicated, but not before we had a minor outbreak in New York City. Luckily, only a few people were infected. Prior to that, smallpox had a long history of sickening and killing people. Those who were lucky enough to survive it were usually left with very serious scarring. The disease taught scientists a lot about how immunity worked, however. Edward Jenner created the first successful smallpox vaccine. You can hear more about how from the video.
When the outbreak occurred in New York City, public health officials realized that a significant portion of the population had to be vaccinated in order to keep it from getting worse. They had to generate over one million vaccine doses in only a few days and more quickly followed. A strategy was used then and has been since in which people are primarily vaccinated after an outbreak happens and so far, it has been effective.