Actually... The vaccine for smallpox was inoculation widely developed during the Napoleonic era, like Polio they vaccinated you by giving you the disease... It disappeared in 1987... And inoculations were first mass produced in 1796, so it took 181 years... But that is a few years in terms of human history.
If you observe attestation papers of men serving during world war 1, many of them will be noted as having an ‘vaccination scar’ from their smallpox vaccination, and I myself have a vaccination scar from receiving the smallpox vaccine in 1967.
My grandfather was almost thrown overboard at sea during WWI . . .I guess the family tree was suppose to continue. . .for such a time as this.
The early cowpox vaccine was crude and not nearly as effective as the modern versions. It also wasn’t widely deployed to most parts of the world until the World Health Organization’s effort at smallpox eradication from 1958-1977. That effort wiped smallpox off the face of the Earth in 9 years.
A disease that killed hundreds of millions of people for thousands of years was eradicated from the planet in less than a decade, once we actually got (mostly) everyone vaccinated.