Vaccination is one of the most important milestones of modern medicine. It has practically eliminated many diseases plaguing the population of all countries for the whole human history. Thanks to vaccination, many infectious diseases nowadays exist only in medical textbooks and historical publications. The number of lives saved worldwide has surely reached hundreds of millions.

Immune response against microorganisms

Vaccination is closely related to the ability of our body to defend against infectious microorganism and produce defensive substances known as antibodies. During the first contact with any dangerous microorganism, our immune system tries to recognize its structure and create a weapon designed specifically against the microorganism. This process takes about a week and during this time, our body defends by less accurate and less effective methods. If the patient survives this critical period, it is probable that the targeted specific immune response destroys the infection quite quickly. The ability to create this type of specific antibodies is maintained and by repeated contact with the same microorganism, defensive antibodies are formed immediately – the infection does not occur at all or it is very short and mild.


The term vaccination comes from the word “vacca” (cow) and it is associated with the invention of vaccination. In the late 18th century, smallpox epidemics raged in Europe. This deadly viral infectious disease has virtually nothing in common with today's chickenpox. The mortality rate in smallpox was high and the survivors were often mutilated with scars all over the body. A very similar, but much less dangerous disease affected the cattle. It has been called cowpox and it was transmissible to humans. British scientist Edward Jenner observed that milkmaids infected with cowpox never get sick of smallpox. He used a sample of pus from the blisters of milkmaids suffering from cowpox and administered it subcutaneously to experimental subjects. It worked – people acquired immunity against smallpox and thanks to global vaccination campaign, the smallpox virus has been practically eradicated worldwide.


The explanation of the vaccination's effect is simple. Cowpox was caused by vaccinia virus, which is in its structure very similar to smallpox. The pus from blisters of sick milkmaids contained vaccinia virus and when applied into the body of another human, this person created antibodies that were effective both against the cowpox and smallpox. Given that the cowpox was not dangerous for humans, there was no great risk of serious consequences or death. When the vaccinated person came into contact with smallpox virus, his body was able to destroy it quickly before the infection could start. This approach became the basis for the so-called active immunization (see below).


Active immunization is the basis of modern vaccination program. It consists of application of  dead or significantly weakened microorganisms or their components that do not cause the disease, but that allows our body to detect its the structure and create antibodies. Our body keeps this capability for case of repeated contact with the microorganism.

Types of vaccines

Vaccines containing attenuated microorganisms

Attenuated microorganisms are simply told weakened and do not cause the disease. However, they teach our body to produce corresponding antibodies.

Vaccines containing killed organisms

They are similar to the previous type, but with killed organisms.

Vaccines containing inactivated toxins

The vaccines are used against diseases where the main danger is related to a toxin. The deactivated toxin is harmless, but it allows us to create antibodies against the toxin's structure. This type of vaccine is used against the tetanus.

Vaccines containing components of microorganisms

This modern type of vaccines is produced by decomposition of certain microorganisms and application of some of these components that allow the production of antibodies.

Special DNA vaccines

These are the latest types of vaccines that are still in the research stage.


Vaccination has saved millions of lives, but we must take into account that it also has certain risks and complications. These include:

Redness and pain of the injection site

This is a relatively common and relatively harmless reaction to the administration of the vaccine. It does not take long and quickly subsides without problems.

Slight increase in temperature

This is also a common reaction that has no special clinical importance.

Allergic skin manifestations

Allergic skin reactions have usually forms of rashes of varying scope and severity.

Anaphylactic shock

This is a very rare complication of vaccination. It is a strong allergic reaction, which is associated with dyspnea and risk of circulatory shock. It must be treated quickly and aggressively, otherwise it may have fatal consequences.


In developed western countries, the public opinion exaggerates the possible harmful effects of vaccination and a tendency grows to prohibit mandatory vaccinations. The potentially harmful effects of vaccines exist, but they must be always taken in the right perspective with millions saved lives. We may say that one child in a million vaccinated may die after vaccination due to a sudden anaphylactic shock, but millions of children's lives have been saved. We do not live in an ideal world and this is a very simple mathematics.


In addition, some people in the population can not be vaccinated (because of severe immunity disorders, etc.) or the vaccine is not functional. Therefore, even in countries with perfectly working mandatory vaccination program, there is a certain percentage of people who are not protected against the particular infection.


It is statistically proven, that such a small percentage does not mind, when the other people are vaccinated. When a substantial part of those other people refuses the vaccination and when the percentage of unprotected people decreases under certain value, the disease can return and cause an epidemic. Such epidemic threatens not only those who refused the vaccination, but also people who can not be vaccinated, or whose vaccine was not effective.


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources