Smallpox was an extremely serious disease that was very common in Elizabethan times. It had very high mortality rates; in 1967 the World Health Organisation estimated that out of the 15 million people who contracted smallpox in that year, 2 million died. It began with a rash, followed by fluid-filled blisters that left survivors with scars, usually on the face (occurring in 65-85% of survivors), and sometimes blindness and limb deformities.
In the Middle Ages smallpox was established in Europe, and by the 16th century it had become very common, especially in disease-ridden London. Even Elizabeth I caught it, but managed to survive with little scarring. After a program of vaccinations in the 19th and 20th centuries, the World Health Organisation was able to declare in 1979 that smallpox is now eradicated from the world.