When using vaccines as one of your management tools, it is important to consider all the potential reasons a vaccination program may fail to prevent disease on your farm. Being aware of the potential problems that can arise will allow a more effective (profitable) means of disease control in your pigs.
The animal - environment - pathogen interaction. One way to envision disease processes in swine is to visualize how the pig , it's environment, and the pathogen or "bug" interact. .
It is easy in a crisis to focus on the vaccine as a silver bullet, but in the face of overwhelming challenge from a pathogen, and poor environmental conditions, even the best vaccines cannot be expected to perform well.
Vaccine failure can occur due to many causes:
Improper mixing of vaccines
Even when a vaccine is administered properly and an immune response occurs, it can fail to protect from disease.
Types of immune response
Antigen that animal builds a response to is not important for disease control
The infectious agent the animal is exposed to is different from that of the vaccine (no cross protection)
The protection of the vaccine has decreased over time so that a low level of pathogen can cause disease
Extreme exposure to the pathogen
VERY little scientific data about vaccine performance in the field.
For some diseases, it is not fully known what antigens and what part of the immune system is important for disease control.
So where does that leave us? With an even larger emphasis on the aspects of disease management that are controllable and are beneficial even in the absence of a disease problem.