How are they different from antibiotics?
Vaccines are used to prevent disease and antibiotics are used to treat existing disease. Vaccines usually have little or no effect on the course of disease once an animal has become diseased. Vaccines can provide long lasting protection against disease where antibiotics provide only weak, short term protection. Antibiotics are chemicals which either kill bacteria outright (bactericidal) or prevent their multiplication in the animal (bacteristatic). Conventional antibiotics do not kill viruses, neither do vaccines. Vaccines sometimes actually depend on bacterial or virus growth to stimulate immunity in the vaccinated animal.
