Edward Jenner introduced the variola vaccine in the late 1700s. Polio didn't even become a major problem until after his death! >In developed countries during

Edward Jenner introduced the variola vaccine in the late 1700s. Polio didn't even become a major problem until after his death! >In developed countries during the late 19th and early 20th centuries, improvements were made in community sanitation, including better sewage disposal and clean water supplies. These changes drastically increased the proportion of children and adults at risk of paralytic polio infection, by reducing childhood exposure and immunity to the disease. (Edward Jenner died in 1823)