Preparations administered to produce immunity are called immunizing agents.

They are known as vaccines, toxoids, and antiserums. Both vaccines and toxoids cause the body to produce their own antibodies (bringing about active immunity), while antiserums produce passive immunity.

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a. Vaccines.

Vaccines contain either weakened or killed microorganisms (such as viruses, bacteria, or rickettsia) that are administered for the prevention, improvement, or treatment of infectious diseases. Examples are typhoid, measles, poliomyelitis, and smallpox vaccines.

b. Toxoids.

Toxoids contain suspensions of modified toxins that have lost their toxicity but which have maintained the properties of combining with antitoxins, or stimulating the formation of antitoxins. Examples are diphtheria and tetanus toxoids.

c. Antiserums.

Antiserums are preparations of blood serum that already contain an antibody or antibodies. They are used when there is not time to wait for the body of the exposed or infected person to produce its own antibodies. Examples are tetanus, immune globulin, and rabies.