What are Vaccines?
Vaccines are drugs used to stimulate your dog's production of antibodies against a virus. If the dog is exposed that particular virus, his immune system will fight and kill any resulting infection quickly. All vaccines employ the same strategy, deceiving your dog's immune system into reacting to the presence of an infection that he doesn't really have. Then the immune system responds by creating immunity to that infection when the dog actually gets it.
There are three general types of vaccines available today; killed vaccines, modified live virus vaccines (MLVs) and Recombinant Technology.
Killed Vaccines
Killed vaccines are made from the dead virus organism. Parts of the dead virus, called trigger proteins, are extracted and make up the vaccine injected into your dog. These proteins get your dog's immune system going to fight the complete living virus, and your dog finally develops immunity to it.
MLVs
MLVs are often more effective than killed vaccines because an inactive form of the live virus is used, and so it behaves like the fully active virus itself. Because the virus is live, (although inactive) there is a small chance that it will revert into the actual disease organism. This is not a common occurrence.
Recombinant Technology
Recombinant technology is a new method where a live virus is taken from a different animal species, where a cross-species infection is not possible. Portions of this virus which the dog's immune system will recognize are then used in the vaccine. Since only these portions are used, the complete live virus can never form in your dog's body, but your dog can develop the desired immunity.
Puppies get their immunities from mother's milk until they are weaned, which is usually when they receive their first vaccinations. If a puppy loses the immunity transmitted through mother's milk before a vaccine is given, that vaccine may fail. A vaccine can also fail if an animal has a fever when it is vaccinated, or if the interval between vaccinations is too short or too long. Steroid use can also cause vaccine failures.
Report any adverse reactions to vaccines to your vet immediately. You can do a service to pets and their owners everywhere if you also report such reactions to the American Veterinary Medical Association, or the US Pharmacopeia, a private organization which collects and reports this data.