How vaccines are made

How vaccines are made

Vaccines are considered to be one of humanity’s most important medical discoveries.

The reason is simple, but not obvious: vaccines have the ability to make us immune to pathogens that, otherwise, would potentially be able to generate real pandemics. Pathogens are infectious agents of biological origin responsible for the onset of diseases.


In short, to the detriment of the slice of population that looks at them with suspicion, the story is clear: vaccines have saved us from several deadly diseases.

Take for example polio, which in the United States alone resulted in the death of over 500,000 people between the 1950s and 1980s. The vaccine, approved in 1962 and created from parts of the dead (inactivated) virus, was able to gradually eradicate its threat.



To fully understand the mechanism of action of a vaccine, it is necessary to dig into its history, going back in time to the second half of the 1700s.

We are in the United Kingdom, where smallpox becomes part of the population’s fears. Smallpox is a very aggressive virus, with a mortality rate of 30%: almost 1 in 3 people die after contracting it.


In 1796 an English doctor named Edward Jenner developed the first true vaccine in history. Dr. Jenner worked mainly in rural environments, and observed a peculiar behavior: farmers, during milking, often contracted smallpox, a much less aggressive form than human. Once healed, these individuals were able to develop immunity to human smallpox. Jenner therefore plans to take a small part of infected material from a girl’s pustule, and to inject it into the body of James Phipps, an 8-year-old boy.

The result is in the history chapters: James contracts the disease, heals it and develops immunity to human smallpox.



What happens in the body of immunized subjects?

Vaccination acts as a trigger for the immune system.

In essence, our white blood cells are stimulated and activated by molecules that are not aggressive in themselves, but which closely resemble the pathogen of interest. These globules specialize and equip themselves to specifically fight that foreign body, until it defeats it.

Stimulation of the immune response conducted through the use of an infectious agent is known as immunization.

What happens next concerns the intrinsic memory of our immune system, which in a nutshell keeps a part of these specialized warriors in the ranks of its army. As a rule, these fighters are quiet in their place, but they activate and reproduce in large numbers if an intruder related to them emerges.



There are different types of vaccines, each with different advantages and limitations depending on the microorganisms to be fought. The preparations may contain parts of the attenuated (live), inactivated (dead) pathogen or only chopped parts. In addition, adjuvants aimed at stimulating the immune response are sometimes added.


Before being marketed, the vaccine undergoes a long research aimed at demonstrating its safety, tolerability of side effects and efficacy in determining a good immune response.


1st step:

It identifies which component of the pathogen is able to optimally stimulate the immune system. The preparation will differ according to whether inactivated, attenuated parts of the pathogen or fragments thereof are used.


2nd step:

Once the preparation is obtained, the preclinical phase begins.

The aim is to understand the toxicity level of the compound and its behavior. The experimentation takes place in vitro, i.e. on cell cultures with extracts of human cells, and then in vivo on suitably selected guinea pigs. In this phase, tolerance and immune response of the vaccine prototype are also evaluated.


3rd step:

Once the preclinical phase is over, we move on to the clinical one, that is, the experimentation on humans. This, in turn, is divided into four steps, three of which are experimental.

The experimental phases are aimed at understanding:

    1. Extent of side effects
    2. Vaccine efficacy
    3. Optimal dose
    4. Scope of the immune response

The fourth and final phase, however, occurs after the marketing of the drug and is called pharmacovigilance: doctors and hospitals periodically send reports to monitor the behavior of the vaccine and any secondary side effects.


The recent Coronavirus epidemic immediately put researchers to work for the production of a vaccine. We delved into the topic in this article:


Coronavirus: first steps towards the vaccine


It can take several years to overcome the process necessary for the marketing of a drug, including vaccines.

Safety must be guaranteed at every step: health is and remains the most important thing to safeguard.


Med4Care Marco De Nardin

Marco De Nardin M.D.





  • Ann Med. 2018 Mar;50(2):110-120. doi: 10.1080/07853890.2017.1407035. Epub 2017 Nov 27.
    Understanding modern-day vaccines: what you need to know.




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