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What is in a vaccine?
A vaccine is used in medicine to enhance or induce immunity to a particular disease. It usually contains an agent that resembles the disease-causing microorganism, and is …often made from weakened or killed forms of the microbe or its toxins. The body's immune system recognizes the vaccine as foreign, and destroys it. It also preserves a memory of it so that, if it encounters it again, it can easily recognize and destroy it in later encounters. Vaccines have been used to eradicate smallpox completely, have greatly diminished the occurrence of many other diseases, and have reduced the death and disfigurement they used to cause. Polio (and the paralysis that it causes ) is now almost a thing of the past, and congenital deformities due to rubella (German measles) is now quite rare. Some vaccines are given after exposure to disease; rabies vaccine is an example of this. Rabies infection was once 100% lethal; it still is if the vaccine is not given in time. There are several types of vaccines, and they are generally made from dead or inactivated organisms (bacteria or viruses), or from their chemical constituents. KILLED: Some vaccines contain microorganisms that have been destroyed with chemicals or heat. Examples include Hepatitis A, influenza, cholera, bubonic plague, polio (Salk injectable vaccine) and rabies. ATTENUATED: Other vaccines contain microorganisms that have been weakened and are no longer virulent, or use very similar but non-disease causing organisms. Most of these are viruses. These vaccines generally produce the strongest and longest-lasting immunity, and are preferred in healthy adults. Examples include yellow fever, measles, rubella, mumps, influenza, tuberculosis (BCG), typhoid and polio (Sabin oral). TOXOID: Some vaccines target the toxic compounds (toxoids) produced by microorganisms which cause illness rather than the micro-organism itself. Examples include tetanus and diphtheria. SUBUNIT: Other vaccines use a fragment of a micro-organism to induce an immune response rather than using the entire micro-organism. These are usually proteins from the capsule of a virus. Examples include hepatitis B, HPV (human papilloma virus which causes cervical cancer) and influenza vaccines are also available in this form of vaccine. CONJUGATE: A newer type of vaccine in which the immune system is taught to recognize the polysaccharide outer coats of some bacteria. An example is Haemophilus influenzae type B (Hib). This organism is a bacterium, not a virus, despite its name. ADJUVANTED: Adjuvanted vaccines for some microbes are available in the US. The US has, however chosen not to use adjuvants in flu vaccinations. But adjuvanted flu vaccines have been safely and successfully used in some European countries for years. These have an additive that enhances the effectiveness of the vaccine, allows for smaller doses since less is needed per dose to get the same immune response, and that saves money per dose as well as allows faster production of enough to go around. In times of a need for rapid development of a vaccine, this helps reduce the dose of each vaccination making a little go a long way. The adjuvant substance is often squalene, made from shark liver oil. There is no proven adverse effect of use of adjuvants, although it is a concern (appropriate or not) of many people. OTHER: Some vaccines have a trace amount of a preservative called thimerosal. This is necessary for multi-dose vials to prevent growth of unwanted organisms. Single dose vials and syringes usually don't need this preservative (in flu vaccines). People have concern about thimerosal because they have heard it contains mercury. There is a trace amount of mercury in the thimerosal, although this has been used without adverse effects. The amount of mercury in a dose of vaccines with thimerosal preservative is equivalent to a meal of fish. The risk of having a problem with thimerosal is much lower than the risk of using a vaccine without a preservative. See also links to related questions about vaccines. (MORE)
