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England:
Edward Jenner. As a child he was inoculated for smallpox, and later in life, at the age of 47, on May 14th, he created the first successful smallpox vaccine.
Before he reached that pinnacle, however, he'd become a family doctor and surgeon, published a study on the cuckoo (in fact; the interest he'd had in Zoology helped him in creating the smallpox vaccine) and earned his MD from the University of Andrews.
Author's notes:
I don't own Hetalia