Immunoprophylaxis is the prevention of disease by the production of active or passive immunity. The incidence of diseases, such as diphtheria, measles, mumps, pertussis (whooping cough), rubella (German measles), poliomyelitis, and tetanus, has declined dramatically as vaccination has become more common.
Vaccination is a cost-effective weapon for disease prevention. Use of vaccines has contributed solely in the eradication of smallpox, one of mankind’s long-standing and most terrible scourges. Since October 1977, not a single naturally acquired smallpox case has been reported anywhere in the world.
Other diseases like diphtheria, pertussis, tetanus, measles, mumps, rubella, and poliomyelitis, also known as “vaccine preventable diseases” have been successfully brought down to negligible levels in most developed nations and in some cases in the developing nations as well.
Active immunization can be achieved by natural infection with a microorganism, or it can be acquired artificially by administration of a vaccine. In active immunization, as the name implies, the immune system plays an active role. Proliferation of antigen-reactive T and B cells results in the formation of memory cells.
Active immunization with various types of vaccines has played an important role in the reduction of deaths from infectious diseases, especially among children. Vaccines may be (a) live attenuated, (b) killed, or (c) in the form of toxoids.
Passive immunization is carried out by administration of human and animal sera, which serve as the readymade source of prepared antibodies against a particular pathogen. These are given to an individual to confer immediate protection against particular pathogen. The immunity, however, is of short duration.
Live Attenuated Vaccines
These vaccines, as the name suggests, contain live attenuated organisms that have lost their pathogenicity but have antigenicity. The attenuated organisms are the suspensions of live organisms with reduced virulence.
These organisms multiply in the body and thereby provide a continuous antigenic stimulus, resulting in production of protective antibodies. Bacille Calmette–Guérin (BCG); smallpox vaccine; oral polio vaccine (OPV); mumps, measles, and rubella (MMR) vaccine; and yellow fever vaccine are some of the examples of live vaccines.
These live vaccines are usually contraindicated for use in immunocompromised patients, such as patients with HIV (human immunodeficiency virus), leukemia, malignancies, etc.
Killed Inactivated Vaccines
These vaccines contain killed pathogens, hence do not replicate in body. At least three doses of killed vaccine followed by a booster dose are essential to confer protective immunity. Typhoid, cholera, pertussis, pneumococcal, rabies, hepatitis B, and influenza vaccines are the examples of killed attenuated vaccines.
Toxoids are modified toxins, which have retained their antigenicity but have lost their toxicity. Adsorption of toxoid to a mineral carrier, such as aluminum hydroxide or aluminum phosphate enhances antigenicity of toxoids. This is because these adsorbed toxoids remain longer in a depot after injection and continue to stimulate immune system of host for a longer period of time.
These are usually prepared by treating toxins with formalin. Two toxoids most widely used for immunization are tetanus toxoid and diphtheria toxoid. DPT (diphtheria, pertussis, tetanus) vaccine is a triple vaccine, which consists of tetanus and diphtheria toxoids and pertussis killed vaccine.
Subunit vaccines are specialized vaccines that are prepared by purifying the fragments of major immunogenic components of microorganisms and are produced by recombinant DNA technology (hepatitis B subunit vaccine).