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."

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."

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."

See also

• Vaccination