Vaccines and Immunization
Passive Immunization
Injection of purified antibody or antibody-containing serum for rapid, temporary protection or treatment of an individual is called passive immunization. Newborns receive natural passive immunity from maternal immunoglobulin that has crossed the placenta or is present in the mother's milk.
Human serum globulin is prepared from pooled plasma and contains the normal repertoire of antibodies for an adult. It is preferable to animal immunoglobulin because there is less risk of a hypersensitivity reaction (serum sickness).
Active Immunization
Active immunization refers to stimulation of an immune response by challenge with an immunogen. Active immunization occurs after each exposure to an infectious agent (natural immunization) and through exposure to antigens in vaccines.
Vaccines are a solution or suspension of materials used to induce artificial active immunity by stimulating the immune system with an antigen that will prevent the disease. Vacines expose the body to a disabled form of a pathogen (or harmless pieces of it), but the immune system reacts as it would to a true assault, generating protective membory cells in the process. Antigens may be organisms, toxoids (modified toxin, rendered nontoxic), part of organisms (capsules) and nucleic acids. The ideal vaccine is one that is specific, safe, long lasting, no side effects, stable, easy to produce and easy to administer. The types of vaccines include the following:
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inactivated microorganism is one that is dead. Killed vaccines are easy to produce and safer. However, killed virus vaccines do not induce cellular immunity and have low levels of humoral immunity. They also require frequent boosting.
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attenuated microorganism is alive and immunogenic but not disease producing. Live-attenuated virus vacines replicate in vivoand induce cellular and humoral immunity. Disadvantages include risk of reversion to virulence. They are also expensive to transport in that they are heat/light sensitive.
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toxoid is immunogenic but not toxic
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macromolecules from pathogens
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recombinant vectors. For example, one can take genes which code for surface antigens for say hepatitis B and transfect yeast cells which will produce those antigens. Recombinant virus vacines are safe in that there is no problem with reversion. As a disadvantage, theimmune repertoire is directed against only a small part of virus protein.
