They introduce disease-signaling proteins called antigens into the animal, so that its immune system produces antibodies. The antibodies remain in the animal, protecting it from disease. Traditional vaccines have some drawbacks. They use the entire disease-causing organism, in an altered form that does not transmit the illness. However, these vaccines contain unnecessary proteins which can cause bad reactions or side effects, and which may interfere with the animal s ability to generate antibodies.
Genetic engineering allows scientists to find the genes which produce antigens.
These organisms copy the necessary antigen in large quantities. There are no unnecessary proteins which might interfere with that process. These antigens are purified from bacterial cultures, improving their safety and effectiveness. The vaccine can be tailored to overcome complicated disease processes. Tailored vaccines offer flexible vaccination times, so animals can be vaccinated when they are likely to be most vulnerable to disease.