Vaccination: principle and history

The vaccine is a preventive drug, the only one available to date, the other drugs being "therapeutic". It is a powerful tool, which has made possible the eradication of certain human diseases on Earth, but which is controversial today for its risks, often out of ignorance. In this article, we will come back to the discovery of vaccination, when it all started.

he principle of vaccination: the discovery of variolization

The principle of vaccination is based on an observation: when a human came into contact with a disease and survived it, he was more likely to resist again against the same disease . An idea then appeared: why not fight evil with evil? If you inoculate in small doses what causes the disease, the body could learn to resist it effectively. This is one of the principles that also founds homeopathic medicine , but we will only deal with one delicate subject at a time!
It was in 1760 that Daniel Bernoulli demonstrated the interest of this practice, already controversial at the time: the treated patients gained a few years of life expectancy . The controversy came from the significant risks of the practice: in 1 to 2% of cases, the patient caught smallpox instead of immunizing against it ... We do not repeat the story, but it often repeats itself anyway.

How does our natural immunity work?

Immunology, the branch of science that studies the biological mechanisms of immunity, is a young science. The understanding of our physiology is advancing rapidly, and we now know many different immunological mechanisms : local reactions or throughout the body, mobilizing complex molecules, or dedicated cells (the famous white blood cells).
The vaccine is particularly interested in the production of antibodies : they are specific proteins, very effective in fighting in particular against viral infections, but also bacterial. Thus, to measure the success or not of a vaccine, and at the same time the protection granted to the individual, it suffices to measure the level of blood antibodies directed against the disease (a serology). If it is above a given protection threshold, then exposure to the disease no longer causes symptoms to appear.
The presence of these antibodies in the body can vary in duration : this is why reminders are used, which are useful for stimulating the immune system again. Naturally, depending on the disease, recall protocols can vary .

How does a vaccine work?

A vaccine is therefore a biological medicine , given as a preventive measure , so that the body can resist an infectious disease on its own .
It is made up of fragments of microbes (viruses or bacteria), or even whole microbes, but dead or attenuated: it depends enormously on the diseases against which we vaccinate. The goal of the vaccine is to trigger a response of the body (and in particular an immune "memory" ) without causing the disease!
An excipient accompanies the vaccine: it is used to transport it , but can also help increase the immune response (by a local inflammatory reaction that attracts white blood cells).

The vaccine is therefore a protective tool which serves both a personal interest (to protect oneself against a disease) and a common interest (to avoid spreading the disease). However, it requires a lot of vigilance because its use is not without risk .

What are the dangers of the vaccine?

A tool is inherently neither good nor bad: it has advantages and disadvantages, depending on the use that is made of it . The vaccine is no exception to this rule, especially since there are sometimes significant differences between the different vaccines.
Indeed, the diseases against which we vaccinate are not the same! And the side effects of the vaccine are very dependent on the symptoms that the initial illness causes . There are two important parameters to take into account:
  • vaccine efficacy : this is the percentage of individuals immunized after receiving the vaccine protocol. Some vaccines treat several diseases at the same time (such as the common cold) and individuals can get sick despite the vaccine, others (such as rabies) are particularly effective and guarantee very good protection.
  • side effects : whether it is due to the microbial agent directly (it depends on the diseases) or to the excipient (sometimes cheaper than healthy), the vaccine, like any medicine, presents a risk. Read this article to learn about good vaccine practices and the dangers of bad practice.
Receiving a vaccine therefore amounts to deciding between the risks of catching a disease (which depend irreparably on living conditions) and its side effects . It depends a lot on the different diseases (whether in dogs or cats ), so do not hesitate to take advice from your veterinarian to receive a consistent and measured vaccination protocol.