Vaccination is an effective way of protecting the masses from harmful diseases before they come into contact with them. It was the simple way her world has eradicated many deadly viruses, including smallpox. It was derived from the old Latin word "vaccinus" which literally means "from the cow".
A long time ago, an English physician Edward Jenner discovered a similar illness in cattle that later got the name "cowpox". The milkmaids in charge of the cows sometimes showed signs of the deadly disease yet could recover quickly and the fatality rate was close to zero.
This led the researcher to find out that the two viruses were similar, but one could kill while the other one could help humans to develop antibodies and become immune. It wasn't the cure she was looking for, but it was the way to stop the smallpox from spreading around and to the rest of the country.
