How can you tell if a dog’s vaccine failed?

If a dog’s vaccine failed, after exposure it can still get distemper or parvovirus—vomiting, diarrhea, cough, runny nose, fever. Also, vaccine side effects like fever, vomiting, diarrhea or allergy can lower immunity and cause failure. Finally, a vet serum antibody test shows if enough antibodies formed; if too low, revaccinate.