Dog vaccines are recommended for several common illnesses, such as rabies and parvovirus, to prevent them from killing young puppies or affecting older dogs. Vaccinations work by inserting a small amount of the virus into the dog to allow the immune system to develop antibodies for that disease.
Natural Antibodies
When a foreign agent, such as a virus or bacteria, infects your dog's body, his immune system develops antibodies to fight off that disease. Once those antibodies have been created, he usually won't be infected by the same strain of that virus again, because his body will immediately recognize and destroy it, more quickly each time.
However, some diseases are so devastating that your dog's body may not be able to fight them off, especially when he's a puppy. These diseases must be introduced in a way that will help him fight them off.
Creating Vaccinations
Scientists have created vaccinations for many common, devastating illnesses, introducing them to the body in small doses to allow the body to become immune to the disease without becoming ill.
Before the virus or bacteria is injected into the dog's bloodstream, however, it is modified so that it can no longer infect the host. In some cases, the virus is first killed, such as rabies, and in others, just rendered inactive. It's important to keep the bacteria or virus intact, because the body responds to large protein molecules of the surface of the infecting agent, and those must be left intact for the body to sufficiently fight off the infection.
Introducing the Vaccine
Vaccines can be given three ways: orally, injections into the blood stream and intranasally (through the nose or eyes). The rabies vaccination is given orally to introduce the entire body to the virus. Vaccines that need a more localized response, such as parainfluenza, which largely affects the respiratory system, are best given intranasally, to best affect the area where they are most needed.
Once the foreign substance enters the body, your dog's body is alerted to the problem and goes into attack mode. Antibodies attack the offending virus or bacteria to render it inactive. Once the virus has been destroyed, the antibodies remain in the body, creating a sort of memory bank for that particular virus.
Most vaccinations are given more than once, which helps the body contine to develop antibodies so it can respond even more effectively. Each time the vaccination is given, the body responds even more quickly. This is why puppies receive the vaccinations early in life and then again later in their adolescence. If the actual virus were to affect them after that, the body would respond efficiently before it could do any harm.
There is some debate as to how long vaccines are effective for dogs. Many veterinarians recommend annual vaccinations, but others suggest that after puppy vaccinations, your dog can retain the antibodies for life. If you are resistant to vaccination annually, titer tests are available to measure the level of antibody in your dog's body.
Regardless, maintaining high antibodies to diseases such as rabies is vital to maintaining the health of your pet and the pet population as a whole.