One of my friends bought purebred pup, 2 days after she brought him home he was in the vets with parvo. It got to the point that they were told to consider putting him down, he was in the vets for over a week with only a drip keeping him alive....no one thought he would make it.
The breeder, with the best intentions, had taken the pup to a show with her a couple of days before my friend picked him up to test he was okay with young children, as at the time she had very young children. The pup had had 2 of the 3 injections. She kept him mainly crated at the show, and only had him out briefly to let some children pat him. Just in that short instant, the pup had contracted the disease (it came out later on that quite a few dogs at that show had also contracted parvo, the vet's other practise in another city had had over 50 cases coming in the next weekend of dogs that went to that show).
No one was to blame, it was just an awful situation and thankfully the dog survived. But it really opened my eyes to how easily this disease can be contracted, and in the future if I ever get a puppy again, I would not take them anywhere until the third injection. I have seen that the risk was too great, and the emotional turmoil that family went through, most of the time expecting that their little pup wouldn't make it.