Just a bit of clarification on the last cases of smallpox and its eradication. It can be a bit confusing because smallpox can occur in two forms, variola major and variola minor. The first is far deadlier than the second which can be milder than chickenpox. They both evolved from the same virus at different points in history, variola minor being first to appear.

top images 1 & 2 / middle images 1 & 2 / final image