Vaccines contain viruses, bacteria or other disease-causing organisms that have been killed or altered so that they can no longer cause disease. Newer vaccines may contain genetically engineered components derived from those disease agents.
It is helpful to learn the basic mechanism of how vaccines work so that there is a clear understanding of the strengths and limitations of vaccines.
All dogs should be vaccinated against those diseases that are widespread, cause serious illness, and are highly contagious. Other vaccines may be recommended based on the risk they pose to individual dogs.
There are other non-core vaccines available to protect individual dogs deemed to be at risk for certain illnesses.