Vaccinations accomplish this by tricking the immune system into thinking that a real infection has occurred. Vaccines should serve as a guide or 'blueprint' so the immune system can build protection and raise resistance. Bacterial infections create illnesses primarily by producing toxins or poisons. Viruses, on the other hand, create illness by destroying the cells in the body that they have invaded. Bacteria are complete living cells which usually live outside the body's own cells and reproduce by enlarging and them splitting in half.
Viruses are extremely small particles which reside inside the cells of the body.
Viruses cannot reproduce by themselves, but rather invade the 'mind' of a cell and reprogram it in such a way that the virus infected cell now is a slave to the virus. It then begins to create millions of new virus particles which will be used to infect other cells of the body. Viruses, by residing inside the host animal's cells, can 'hide' from the immune system. Booster Dose Vaccine Types T able 1 lists some of the common infectious agents of cattle and categorizes them as either viral or bacterial. Table 2 lists the various types of vaccines available for each of the two groups.