The purpose of a vaccine is to provide the person receiving it with immunity to a particular microorganism. These vaccines are injected into the bloodstream of the person, sometimes at an early age. In some cases, they give lifelong immunity, but in other cases, the vaccination must be repeated at regular intervals. The point, though, is to keep the person disease-free from some of the most damaging entities that humanity faces such as the influenza virus, for example. Ultimately, an appropriate vaccine could even spell the end of HIV, although this seems some way off yet.
Most people would agree that vaccination is a vital advance in medicine. The method of vaccination involves taking a particular microorganism that you want a person to be immune to and providing them with it by injecting it into their bloodstream, for example. In doing this in a controlled and understandable way with known results, the immune system can be provided with the information that it needs to produce antibodies that will kill live and dangerous versions of the microorganism that it encounters in the future. In other words, they become artificially immune to the disease without having to catch it naturally.
One of the techniques involved in vaccination programs sees the use of small amounts of live examples of the microorganism that you want the person to be protected against. A second way involves an attenuated version of the entity. Here the structural information can be used by the immune system but with there being key aspect of the entity's physiology deactivated so that they cannot cause the disease. Another approach features killed microorganisms. The structural information that will be useful to the immune system is kept, but infection is not possible.
An example of a live vaccine is that of the Sabin polio virus vaccine. An example of an attenuated vaccine is the MMR vaccine, which covers measles, mumps, and rubella, and has caused a lot of controversy in recent years over its safety. However, there is no real evidence for these concerns.
Examples of killed microorganism vaccines include those for influenza, bubonic plague, and hepatitis A. All of the diseases mentioned here and many more like them can already be prevented or cured by vaccination. Many more great killers such as HIV and cancer, for example, will also be prevented and cured in the future as medical technology and techniques progress.