A short and interesting video on how we eradicated Smallpox.
Link: https://www.youtube.com/watch?v=ybVZ7vluYhQ
Note that "eradicate" is perhaps a bit severe, the disease lies dormant in many labs and permafrosts, and current defunding by the US of Vaccines and WHO in general may well bring it back. But - for a time, when we trusted the experts and good science, it was gone.