Actually, wagging of the tail is a good sign. Parvo is so dangerous in puppies because it dehydrates and leaves the animal a wasteland (from not eating or getting nutrition). It's a virus that kill off cells and divides rapidly among them. This lack of nutrition leaves the animal weak beyond weak with NO energy. The IV fluids have helped tremendously and if the pup is wagging its tail, that means it's getting better. That's what i know from my experience. I vaccinate my animals but i've had a few too many encounters with people who don't vaccinate and end up here. If the dog overcomes, she probably won't ever have a need for the vaccination because she'll be immune. Have you tried searching anything? This link will help with all your questions.
Parvo FAQs