Many vets recommend vaccinating puppies every three to four weeks for this virus starting at 6 weeks of age and continuing until they are at least 16 weeks of age and preferably 20 weeks of age. It is possible that this vaccine confers lifelong immunity once it does work but most veterinarians continue to recommend yearly vaccination for it. It seems prudent to at least get the vaccination at one year of age. Since it is combined with the other vaccines it is often easier just to give it yearly with them. It causes dogs and puppies to not be able to absorb nutrients or liquids.
Puppies are especially prone to it because they have an immature immune system.
When dogs and puppies contract parvo, they often have diarrhea, vomiting and lethargy. Usually they stop eating and develop a bloody, foul-smelling, liquid stool. Symptoms usually begin with a high fever, lethargy, depression, and loss of appetite. Secondary symptoms appear as severe gastrointestinal distress, such as vomiting and bloody diarrhea. In many cases, dehydration, shock, and death follow.