[In this painting we see Jenner using cowpox to inoculate against smallpox. He performs his very first vaccination on 8-year-old James Phipps on May 14, 1796. Painting by Ernest Board.]
Now what is the idea of “variolation” ? Here it is:
In a variolation, a doctor transferred smallpox pustules from a sick patient into a healthy one because—for reasons no one at the time understood—a variolated patient typically developed only a mild case of smallpox while still gaining lifelong immunity.
This fact was known for a long time in the medieval farmer community: there, it was well-known that by milking cows (some of which had cowpox), one was protected from human smallpox.
But Jenner was the one who found a medical-scientific mechanism behind it.
And he was consequently the person to invent the principle of vaccination: treating a patient with a less virulent pathogen / immunogen (whereas in inoculation one is using an unattenuated virus).
One of the deadliest diseases in history, more than 200 million humans are estimated to have died from smallpox since 1900 alone.
And thanks to a massive global vaccination campaign in 1977, an end was put to the disease.
Making it the very first disease believed to have been ever eradicated.
Thanks to farmers, cows and Jenner.
And democracy.