Smallpox killed as many as 10% of all the human beings that have ever lived. I've seen that as high as 20%. Today there is a conversation on the ethics of destroying the last live samples of Smallpox, which today lives in two laboratories: one in the US and one in Russia.
In 1967 the World Health Organization, along with multiple governments, pushed to get rid of one of out biggest mass murderers. Smallpox was declared eradicated in 1980. Smallpox is terrible and we are better off that it is gone.
Not so much a science, although the science behind vaccines is amazing, but I put this story out there to show what we can do on this spinning ball of rock once we put all the nonsense away and get down to the work.
WHO page on Smallpox