My vet explained to me that dogs, like children, are given a series of booster shots that are temporary. Because vaccines are taken from an actual virus, they can only be introduced slowly in a small animal, or an infant. Once the puppy has built an immunity, through the boosters, the final dose is given to make them completely immune. I have 2 different vets, one for my beagles and one for my Yorkie (she specializes in Yorkies) and they both agreed that the first 3 shots that puppies are given are only "boosters". This shows the importance of following through with full vaccinations. I could be totally wrong, but I hope this helps.
Shelley and Rocky Balboa
