Vaccination is the process of introducing an external agent (the vaccine) in a living organism to create a positive immune response against infectious disease. The active ingredient in a vaccine antigen is designed to stimulate natural defences of the body (the immune system). There are four types of vaccines according to their preparation: infectious agents inactivated agents live attenuated, subunits of infectious agents or toxins inactivated.

History of vaccination
From the eleventh century, the Chinese practiced variolisation: inoculate it was hoped that a few of virulent smallpox in bringing together the person to immunize with the content of the substance suppurant vesicles of a patient . The result, however, remained uncertain and risky, the mortality rate could reach 1 or 2%. The practice has gradually distributed along the Silk Road. It was imported from Constantinople in the West in the early eighteenth century. In 1760, Daniel Bernoulli showed that, despite the risks, widespread this practice would earn a little more than three years of life expectancy at birth.

For the first time, years 1770 until 1791, at least six people were tested, each independently, the ability to immunize human smallpox in their inoculant smallpox cows, who was present on the udder of the cow. Among those who took the first tests appear in 1774, an English farmer on behalf of Bejamin Jesty, and in 1791, a German schoolmaster on behalf of Peter Plett. In 1796, English physician Edward Jenner will make the same discovery and will fight so that we officially recognize the good result of immunization. On 14 May 1796, he inocula to a child pus taken from the hand of a farmer infected with vaccinia, or smallpox cows, who was present on the udder of the cow. Three months later, he inocula smallpox to the child who has proved immune. This practice has spread gradually across Europe. The word vaccination comes from the latin vacca which means cow.

The principle of action of vaccination was explained by Louis Pasteur and his colleagues Roux and Duclaux, following the work of Robert Koch putting together germs and diseases. This discovery allowed him to enhance technology. His first vaccination was the vaccination of a flock of sheep against coal May 5, 1881. The first human vaccination (except vaccination in the original sense of Jenner) was that of a child against rabies on June 6, 1885.

Principle of vaccination
The main goal of vaccines is to induce production by the body of antibodies, biological agents natural defence body vis-à-vis pathogens identified. A vaccine is therefore specific to a disease but not to another. This antibody production gradually decreases in a period longer or shorter, thus setting the duration of effectiveness of the vaccine. It is measurable and this measure can be applied in some cases whether the subject is vaccinated effectively (hepatitis B vaccine and anti-tetanus in particular).

Antibodies are produced by B lymphocyte differentiation in plasma. The number of B cells memory, but not secreting respond specifically to the presentation of an antigen, appears to him, do not vary over time.

But some vaccines do not cause the formation of antibodies but involve a reaction of so-called protection cells, is the case with BCG (Bacillus Calmette-Guerin ", anti-tuberculosis vaccine).

The immune system and "stimulated" by the vaccine prevent an attack by the pathogen for a term which may vary from one vaccine to another. This prevents the development of an infectious disease at the individual level and in the case of a contagious disease and a mass vaccination, the level of a population.

Ideally, vaccines should be inoculated as healthy people because of side effects more or less severe can be seen with a variable frequency. They may however be administered to people with chronic diseases who are particularly sensitive to certain infections (cases of influenza vaccination of patients with respiratory diseases).

Types of vaccines
Vaccines are usually inoculated by injection, but they can be orally (which has helped nearly eliminate the rage of Europe with 12 per bait vaccine against rabies in foxes distributed in nature) and vaccines by nasal spray are being tested (eg flu vaccine NasVax Israel).

The matter vaccine itself is classified according to its nature into four categories:

Vaccines derived from infectious agents inactivated
Once the infectious agents identified and isolated, they multiply in large numbers before destroying them chemically or heat. In this way vaccines are produced by example against the flu, cholera, plague and hepatitis A.

Vaccines derived from live attenuated agents
The infectious agents are multiplied in the laboratory until they lose naturally or artificially, by changing their character pathogen. The strains are then obtained unable to fully develop the disease before they cause, but nevertheless retain their antigens and their ability to induce immune responses. This type of vaccine is generally more effective and more lasting effect than the one which is composed of infectious agents inactivated. But as it is made up of micro-organisms whose viability must be maintained to be effective, its conservation is also more difficult. As examples of this type of vaccine can include vaccines against yellow fever, chickenpox, rubella, mumps, measles, tuberculosis (BCG), a Rotavirus gastroenteritis.

Vaccines made of subunits of infectious agents
These vaccines, instead of containing the entirety of infectious agents, shall include only constituents they needed to obtain immune responses.
For example, vaccines against hepatitis viruses B or against the human papillomavirus and are made of proteins which are naturally to the surface of these viruses. Another example is the vaccine against pertussis, infectious disease caused by the bacterium Bordetella pertussis. Generally, yeasts modified by genetic engineering to produce large quantities of proteins of interest, are used in the manufacture of these vaccines.
Beginning in May 2008, Denis Leclerc proposed to use a plant virus (which can not be repeated in humans) as pseudovirion playing the role of adjuvant, to make vaccines more effective at length against viruses which often mutate (influenza virus or hepatitis C, even against some cancers. The idea is to combine this pseudovirion a protein target internal viruses, bacéries or cancerous cells to attack and not as is done hitherto an external proteins are those that mutate most. This new type of vaccine, which has yet to be proved its safety and efficacy, would trigger an immune reaction inside cells during the viral replication.

Vaccines made of inactivated toxins
When the most serious symptoms of the disease are due to toxin production by the infectious agent, it is possible to produce vaccines only from these toxins by inactivating chemically or heat (a toxin and is rendered harmless then frequently called a "toxoid" or more generally a "toxoid"). The tetanus or diphtheria are two examples of diseases whose symptoms are caused by toxins and against which vaccines are produced in this way.

Other additives may strengthen the immune response.

Preventive vaccination
Preventive vaccination is a form of vaccination to stimulate natural defences to prevent a disease. It never ceases to see expanded its field and can prevent diseases following:

* Diphtheria, tetanus, pertussis, polio, meningitis due to the germ Haemophilus influenzae serotype b, hepatitis B, influenza, tuberculosis, measles, rubella, mumps, pneumococcal ...

The number of diseases that were trying to prevent from an early age in France has continued to grow and it will doubtless in the coming years to introduce other, which makes it simpler by example using vaccines "multivalent" (ie, effective against various diseases at the same time) to avoid delays and dropouts.

The large-scale vaccination can reduce significantly the incidence of disease in the vaccinated population, but also (if the transmission thereof is only inter-human) in that it is not, the human reservoir of the germ becomes very small. The eradication of polio type 2 in 1999 is attributed to the vaccination campaigns.

Contrary to popular belief, the role of vaccinations in the eradication of smallpox in 1980 would be minor according to a report issued by the WHO. It would appear that a strategy of containment and surveillance put in place in early 1970 has been more successful in eradicating this disease.

Vaccination therapeutic
Also called immunotherapy active, this technique is to stimulate the immune system of the body to promote the production of antibodies. It does more to prevent the emergence of a disease but to help the body of persons already infected in the fight against the disease by restoring its immune defenses. Contrary to popular belief, vaccination against rabies is not therapeutic. In fact, pre-exposure (in people who may be affected because of their professional activity, for example) it is a usual vaccination (injection of antigen which will stimulate the manufacture of specific defenses). In post-exposure, ie after a bite by an animal may be rabid, it is a passive and active immunization. Passive because there injection of immunoglobulins (antibodies) against specific rabies and at the same time injection of rabies vaccine. Unlike AIDS or cancer, anti-rabies vaccination is far more at an experimental stage.

The anti-polio vaccine
The first mass vaccination campaign anti-polio in 50 years, was marked by an important provision of defective batch (non-attenuated live virus) leading to nearly 220 000 infections including 70 000 patients, 164 severe paralysis and 10 deaths

* Risk of transmission to the entourage (if vaccine based on live attenuated viruses)
* Contamination by the unfortunate SV40 (simian virus 40 (virus harmless to monkeys but carcinogenic to humans, although to date, no study has demonstrated an increased risk of cancer in those who received the vaccine contaminated)
* Dermatites generalised
* Joint pain near the injection sites
* Anaphylactic Reactions
* Reactions neurological: convulsions, polynévrites, transverse myelitis, facial paralysis, Guillain-Barre, sclerosing panencephalitis subaigüe
These techniques are still experimental. It is hoped that they can help in the fight against diseases such as AIDS and cancer.

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