Vaccine

Vaccines are "suspensions of killed or attenuated microorganisms (bacteria, viruses, fungi, protozoa, or rickettsiae), antigenic proteins derived from them, or synthetic constructs, administered for the prevention, amelioration, or treatment of infectious and other diseases." They are expected to produce a detectable immune reaction, such as a rise in a specific immunoglobulin, that assists the body in preventing infection. "Therapeutic" vaccines are administered in the presence of active disease, but do not directly have an effect on the pathogen. Therapeutic vaccines augment bodily response.

Antitoxins, drugs using monoclonal antibodies, etc., which directly attack or neutralize the pathogen or its effects, are immunologic treatments, but they are not in the category of vaccines.

History

Vaccines, in one form or another, have been used for several hundred years. Buddhist monks drank snake venom in an attempt to resist it later. Chinese men once wore the underwear of the diseased with the hopes of immunization (though to questionable effect). Using the disease to directly infect a person is called variolation, with the intent of resisting the same disease later.

Edward Jenner, in 1796, was the first person known to use something other than the disease itself. He heard a tale of a village that did not get smallpox - where the people often worked with cowpox infected cattle. After several experiments he proved this to be true. Afterwards he cultured cowpox and offered it to villagers. He was so confident that this method prevented smallpox that he also inoculated himself, his wife, and all of his children. None of them ever contracted smallpox. "

Classification

Complete microorganisms

Live, attenuated microorganisms

These vaccines are "live vaccines prepared from microorganisms which have undergone physical adaptation (e.g., by radiation or temperature conditioning) or serial passage in laboratory animal hosts or infected tissue/cell cultures, in order to produce avirulent mutant strains capable of inducing protective immunity."

Examples of live attenuated viruses include the herpes zoster and measles vaccines and the bacillus Calmette-Guérin (BCG) vaccine.

Inactivated microorganisms

These are vaccines "in which the infectious microbial nucleic acid components have been destroyed by chemical or physical treatment (e.g., formalin, beta-propiolactone, gamma radiation) without affecting the antigenicity or immunogenicity of the viral coat or bacterial outer membrane proteins."

An example of inactivated vaccines is the polio vaccine.

Components of microorganisms

Component vaccines include naturally occurring and synthetic materials.

Toxoids

Toxoids are "preparations of pathogenic organisms or their derivatives made nontoxic and intended for active immunologic prophylaxis. They include deactivated toxins." They confer active immunity but do not directly counteract the effects of the pathogen, as do antitoxins or monoclonal antibodies that kill organisms, passively add immune defensive factors, or neutralize toxins. Antitoxins provide temporary passive immunity.

Synthetic

These vaccines are either peptides or DNA and are defined as "small synthetic peptides that mimic surface antigens of pathogens and are immunogenic, or vaccines manufactured with the aid of recombinant DNA techniques. The latter vaccines may also be whole viruses whose nucleic acids have been modified."

Synthetic vaccines include conjugate vaccines which are "semisynthetic vaccines consisting of polysaccharide antigens from microorganisms attached to protein carrier molecules. The carrier protein is recognized by macrophages and T-cells thus enhancing immunity. Conjugate vaccines induce antibody formation in people not responsive to polysaccharide alone, induce higher levels of antibody, and show a booster response on repeated injection." conjugate vaccines include the Neisseria meningitidis and pneumococcal polysaccharide vaccines.

Synthetic vaccines include DNA vaccines which are "recombinant DNA vectors encoding antigens administered for the prevention or treatment of disease. The host cells take up the DNA, express the antigen, and present it to the immune system in a manner similar to that which would occur during natural infection. This induces humoral and cellular immune responses against the encoded antigens. The vector is called naked DNA because there is no need for complex formulations or delivery agents; the plasmid is injected in saline or other buffers."