Actually, the discovery of vaccination in the first place, you might remember, was for smallpox, and it was the recognition that women working as milkmaids seemed to be protected against smallpox, having had cowpox. They tried infecting people with a bit of cowpox virus and the funny thing was that those people didn't get smallpox. So it really is exploring nature for hints as to things that can make a difference.
On October 26th, 2009. See this statement in context.