This is Scientific American's 60-second Science, I'm Susanne Bard.Smallpox was eradicated worldwide in 1980. So generations of people have never had to experience the devastation the disease once brought."It could cause, sometimes, even in excess of 30 percent mortality. It caused these very painful blisters that covered the entire body."McMaster University's Ana Duggan. She studies how genomes evolve.The first vaccine for smallpox was developed in 1796.It worked by infecting people with pus from pox lesions caused by similar but far less pernicious conditions, like cowpox.At the time, no one knew that viruses caused these diseases."We didn't have microscopes that were strong enough to see them.So we had physicians that were performing this procedure that they knew was beneficial.But they didn't understand why it worked. They just knew that it worked."Smallpox vaccination became common in the 19th century. During the American Civil War, all new soldiers on both sides were required to be vaccinated."You had a large number of individuals who were congregated in a single place, such as an army barracks, where a disease can spread very easily."Back then, there were no mass-produced vaccines.Instead physicians often used fluids and pox scabs collected from previously vaccinated people and shared these materials with each other.They were kept in custom-made vaccination kits―a leather case containing a tin box, glass slides and a lancet for scratching the skin to introduce the vaccine into the body.