Prevention of certain infectious diseases by immunization has become an established part of medical practice. Active immunity produced by the introduction of an organism or its products into the body predisposes to the more rapid development of the formation of antibodies on subsequent exposure to that particular antigen. This is preferable to passive immunity because of its long duration and because usually no animal serum is used to which the recipient might be sensitive or sensitized. Passive immunity, although highly effective, has definite limitations because of its nature. It is of temporary duration, it must be given at the proper time or interval, it usually sensitizes the recipient to the serum of the animal from which it is derived or the recipient may already be an allergic person.
Active immunization of infants and children against diphtheria is now generally performed. The practical value of this procedure is so well known
BIGLER JA, WERNER M. ACTIVE IMMUNIZATION AGAINST TETANUS AND DIPHTHERIA IN INFANTS AND CHILDREN. JAMA. 1941;116(21):2355-2366. doi:10.1001/jama.1941.02820210001001