Routine vaccination of young puppies should take place within the first 16 weeks to one year of their life, during this time there are a lot of changes in the immune system of the animals. New born puppies must obtain passive immune protection through the ingestion colostrums within the first hours of life. Timing the early vaccination is determined by the amount of time required for passively acquired immunoglobulin to degrade thereby permitting an endogenous immune response to be generated. Adaptive immunity to viruses develops earliest and is highly effective. Such anti viral immune responses often result in the development of sterile immunity and the duration of immunity is often lifelong. Also adaptive immunity to bacteria, fungi, parasites develops more slowly and the duration of immunity is generally short compared with most systemic viral infections. Old dogs rarely die from vaccine preventable infectious diseases, especially when they have been vaccinated and immunized as young puppies (16 weeks to 1 year). However young animals do die because either vaccines were not given at all or not given at the appropriate age, too early in life in the presence of maternally derived antibody. If a dog has had its proper vaccines in the young age and at the right time then studies show that even if the dog was not revaccinated for as long as 9 years, these animals had serum antibodies to canine distemper virus, canine parvovirus type2 and canine adenovirus type 1 (these are major canine killer diseases) at levels considered protective and if these dogs came in contact with these diseases the dogs immune system resisted the infection or disease.