Physicians and researchers overwhelmingly agree that animal systems provide invaluable and irreplaceable insights into the human system because of the striking similarities between human and animal physiologic systems. And where there are differences between animals and humans, the study of animals tells us how and why things work as they do. In the beginning, much of what was learned about vaccination and the human immune system resulted from the successful development of veterinary vaccines against rabies, anthrax, cowpox--diseases that are readily transmissible from animals to man.

Animal models have been critical to understanding the basic biology of microorganisms. Knowing the mechanism(s) by which an organism produces disease is vital for designing vaccines to protect people. Two new scientific disciplines - genomics and proteomics - that investigate the structure and function of the genes and proteins expressed by disease producing organisms help scientists in their quest to identify targets that the immune system can recognize as harmful.

Animals have also been critical to determining how the immune system works. Scientists have been able to identify and describe the protective network of specialized organs (thymus, spleen, bone marrow lymph nodes) that produce different types of lymphocytic cells and a variety of antibodies and cytokines (small signal proteins that regulate immune activities) which are called into play when the body encounters a pathogen.

And finally, animals have played a vital role in detecting desirable and undesirable features of a newly developed vaccine. Patient ready vaccines may take years of testing to develop. Strict regulations prevent a vaccine from being used in humans until it passes tests for safety in preclinical evaluations in animals (e.g. rats, mice, nonhuman primates). Usually, it must also pass tests for efficacy in animals before evaluation in larger clinical studies to determine efficacy in humans. Scientists also rely on animals to learn how to enhance the immune response by determining the quality of the antigen, the route of injection, and the dosage required to elicit an optimal response.