Can you provide documentation for this? I have never heard it asserted before that immunity is possible absent vaccination.
I read this book, Scourge: The Once and Future Threat of Smallpox maybe a month after it was published on September 2, 2001. It has excellent information about the history of smallpox, it's effects, it's use as a weapon of war, the erradication campaign in the 1960s and '70s, the biowarfare program that the Soviet Union had to make it into a doomsday weapon, and the possibility of smallpox getting into the hands of rogue nation or terrorists. I read the book during the middle of the anthrax attacks in Ocotber 2001. Everthing I mentioned is documented in this book.