If you’ve ever gotten a puppy, you probably know that it is supposed to get vaccinated. But you may wonder what the vaccines protect against and why they need to be vaccinated so many times at such a young age.
The typical “distemper” shot puppies and adult dogs receive is not just for the disease known as canine distemper. It covers five diseases with one vaccination, which are distemper, adenovirus, parainfluenza, parvovirus and leptospirosis. A big one for puppies is parvo, because it causes a dangerous intestinal disease that can kill puppies.
Now in older dogs, the vaccine needs to be given fairly infrequently. Since the adult animal has a developed immune system, they have an effective response to the vaccine that protects them well against these diseases.
Puppies, on the other hand, have an immature immune system. Even though they receive the same vaccination at the same dose as an adult, the puppy immune system does not react as strongly to the vaccination. Consequently, they do not build immunity as well from a single shot, and need boosters to create an additive effect that protects the puppy.
This chart shows how this works. The first shot gives the puppy some immunity, but not enough. Each successive shot adds to that immunity, so that by the time the third shot is done the puppy has reached a level of protection that should keep these diseases at bay. So if you have the fortune of getting a new puppy, make sure it gets all three rounds of its shots, plus the rabies vaccine, to keep it happily frolicking in your backyard.