Answer:
Vaccines contain a substance called antigen. Antigen makes the body react and produce protection. Vaccines may contain different forms of antigen. Vaccines may be made from weakened germs so that they cannot cause the disease, from a toxin produced by a germ treated to make it harmless, from only part of the germ, or may contain part of the sugar coat of the germ joined with a protein to make it more effective. Besides antigen, vaccines contain other substances. Live vaccines contain small quantities of antibiotics, whereas dead vaccines often contain preservatives designed to kill any germs that might accidentally get into the vaccine.