answer:If the puppy isn’t exposed to worms, or rabies, or distemper, or parvovirus, the puppy could go indefinitely without getting sick—just as a human who hasn’t been inoculated against measles and polio who’s never exposed to those two diseases won’t necessarily get sick. But where a vaccinated dog who’s exposed to parvovirus, for instance, won’t even come down with it, an unvaccinated dog will probably die of it. Your friend is not being a terribly responsible dog owner. What about rabies shots, or spaying and neutering?