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How we fight bacteria: Vaccination (Immunization)

Bacterial infections activate our Immune system, and approximately two weeks after the start of an infection, antibodies are produced. These are proteins in our blood that help white blood cells to recognize the infectious organisms and to destroy them. This ability, to specifically recognize and destroy micro-organisms, is stored in the memory of the antibody producing cells, and this is what makes us immune to that particular infection. Next time those bacteria enter our body, they will be destroyed immediately and no longer can make you ill. This acquired immunity will not only result from an infection; it can also be induced by vaccination.

It was Edward Jenner who tried the first experimental vaccination. He recognized that certain people never got small-pox, and realized that they had been exposed to the less severe disease of cow-pox. His experiments showed that injection with cow-pox virus could make people immune to small pox. The way this works is simple: the cow-pox virus is very similar to the small-pox virus, and when antibodies are produced against the one, they will also act against the other. Louis Pasteur (Source: Biotech) continued this research and tried his vaccines (amongst others agains rabies) on a number of people, but it was very crude and actually made people quite sick. Nowadays it is possible to produce safe vaccines.

A vaccine is a weakened, killed or incomplete form of a micro-organism that cannot cause disease, but will result in the production of antibodies when it is injected in our body. As a consequence, the produced antibodies will protect us against that disease. Since our body can make antibodies against viruses and bacteria, we can get vaccines against viral and bacterial infections.

Read more about infections and vaccinations (Source: Dr. Reddy's pediatric office)
Read about the different kind of vaccines and how they are developed (source: Ultranet, EJ Kimball).

When a vaccine consists of a weakened or killed form of a bacteria or virus, it is important that this is so disabled that it can absolutely never cause disease. In many cases it is preferred to use a vaccine containing only part of the microorganism, or one of its key products that would be formed in our body during an infection. In that case the risk is minimal, and the effect can be sufficient immunity. Often repeated injections are needed, and after several years a 'booster' will refresh the memory of our immune system. Some parents worry about the risks of vaccination. No injection is without the risk, however, the diseases they are protective for are far more risky. Know your risk: vaccinations and the diseases they prevent (Source: iVillage, with apologies for the advertisements appearing before the information).

Vaccination has been a key solution to reduce the incidence and mortality of infectious diseases. See our special feature file on the history of infectious diseases to read about the epidemics that ruled the world before vaccinations, in combination with better hygiene and medication, gave us the weapons to combat infections.

The development of new vaccines (Source: World Health Organisation)
The National Immunization Program of the USA (Source: CDC)
In one case, vaccination resulted in a world-wide eradication of the disease: small-pox. How did they do it? (Source: Uni leicester, UK)
Information on vaccination by the Immunization Action Coalition, an organization trying to boost vaccination rates

So why don't we vaccinate against all infectious diseases? And why do infectious diseases still exist? Several diseases can be caused by many different kinds of the same sort of bacteria. For instance, traveler's diarrhea is often caused by E. coli, but there are many different forms of E. coli, and when you have had one (which may have been bad enough to spoil your holiday) you are not yet protected against the rest. In that situation vaccination is not very efficient. Moreover, some bacteria are smart enough to evade our antibodies. They change their 'looks' constantly, so that antibodies produced to one variant are useless towards the next. When antibodies are powerless, vaccines are as well. And there is an economic aspect: vaccination is expensive, and especially in developing countries it is not possible to reach the majority of the population with vaccination programs. Vaccination is not completely without risk, and it would be unwise to inject everybody with all available vaccines, when the majority of those people have very little risk to ever get most of these infections. So when you live in a moderate climate, you will not be vaccinated against tropical diseases, unless you plan to travel in the tropics. Check out vaccination recommendations for travellers (source: CDC). And finally, for many infectious diseases a vaccine is not (yet) available. Vaccine development is one of the major research areas in medical microbiology.

The content of this page is copyright of the Virtual Museum of Bacteria and was written by Dr. T. M. Wassenaar (curator), with support of the Foundation for Bacteriology.

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Page last modified: 09 Mar 2006

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