In December 1979, smallpox was
officially declared eradicated but it had already happened by then, thanks to the efforts of giants like Drs. Don Henderson and Bill Foege, not to mention 150,000 international workers pushing the disease first out of Europe and Asia, then to the Horn of Africa, and finally out of existence.
The last case was known in 1977 but no one was willing to raise any glasses, yet
by early 1979 everyone knew the clocking was ticking. Finally, by the end of the year it was official. Smallpox was gone, and vaccines had done it. But not without help from those 150,000 pairs of boots on the ground and ... math.