Vaccines are highly effective in preventing certain infectious diseases in dogs, but failures do occur. Failures can be due to improper vaccine handling and storage, incorrect administration, inability of the dog to respond because of a depressed immune system, or the presence of neutralizing maternal antibodies.
Stretching out the vaccine by dividing a single dose between two dogs is another reason why a vaccine may not be effective. And if the dog is already infected, vaccinating him will not alter the course of the disease.
Because proper handling and administration of vaccines is so essential, vaccinations should be given by those familiar with the procedure. Anyone giving a vaccine also needs to be ready to handle any adverse reactions. When you go to the veterinarian for your dog’s annual physical examination, he will also receive any vaccines that need updating.