Not really, you can't fight off something like smallpox if you've never been inoculated. That inoculation can, however, occur organically and naturally as opposed to artificially. This is why Europeans could carry smallpox to the New World. Trust me, I get what you're saying - I'm just adding the point that using dangerous pathogens to help people medically is neither new nor unusual.
"Kids?! I can't find the remote and I refuse to stand up!"