However, it is more likely they will come down with the disease and die from it, or have a prolonged illness. Vaccination with products that don't cause the disease, but cause an immune response is in my estimation the better road to follow. If the animal does not come in contact with the antigen it will never develop immunity. No species is comprised solely of members who are susceptible to a pathogen. Some pathogens simply cannot infect certain individuals, not due to antibody response but due to the fact that they are not susceptible to that particular pathogen.
All vaccination does is replace acute illness with chronic disease.
Naturally reared, well-bred animals can encounter illness and either develop immunity without getting sick, as mine do, or they can suffer a brief acute illness and then develop immunity. Encounters with illnesses are good for animals. If an animal literally succumbs to every pathogen it encounters, it's either being raised abysmally or it's genetically very unhealthy. Vaccines cause more problems than they prevent, but the fact is that most pets in this country are not healthy enough to fight off disease anymore. Vaccines do nothing but prevent the body from expressing a normal immune response to acute illness.