September 28, 2020
2 mins read

Phases in the development of a vaccine


For a vaccine to reach pharmacies or hospitals, you have to go a long journey of many years. The pandemic caused by the Sars-Cov-2 virus that causes  Covid-19  disease has shaken the world as well as pharmaceuticals. There is a global claim to produce a vaccine as soon as possible to better combat the virus, immunization of the population.

This rush to find a vaccine as soon as possible is not good because a vaccine has to be 100% effective  and  100% safe. Introducing into the human body a substance that activates our immune system cannot be something that is taken lightly. We may encounter unwanted side effects that can jeopardize the life of the individual who took the vaccine candidate.

Most governments now allocate more resources to fight the virus. And this increase in spending will increase in the coming years. Health is going to be increasingly important, among other things because pandemics like today may be repeated in the future.

Drug approval process

Developing a drug that will lead to a vaccine is a long process. It can be up to 11 years from the time a target is identified to the introduction of a new vaccine. In addition, a large majority of candidate drugs do not reach the market. Approximately 1 in 9 drugs tested  is marketed.

The steps to make a vaccine take an average of 6 months and would be:

  1. Isolate the pathogen. The Sars-Cov-2 virus was ingsed in January 2020..
  2. Grow it in culture media.
  3. Inactivate the virus.
  4. Make vials with preservative and adjuvant. Adjuvants are substances that help activate the immune system.
  5. Efficacy studies in animals and volunteers.
  6. Approval by the European medicines agency in Europe or similar in other parts of the world.

For example,  the polio vaccine has two types. The first was developed  by Jonas Salk, tested in 1952 and began commercialized in 1955 (3 years). It involves injecting inactivated or dead polioviruses. The second vaccine was oral developed by  Albert Sabin and in this case attenuated poliovirus was used. Clinical trials of the Sabin vaccine began in 1957 and was authorized in 1962 (5 years).

An inactivated vaccine consisting of particles from a pathogen that have been grown in cell cultures and that lose the ability to produce the disease. On the other hand, a  attenuated vaccine is a vaccine that seeks to reduce the virulence of a pathogen. The pathogen is altered to be harmless or less virulent. In both cases the immune system works by creating antibodies to recognize and kill the virus.

The use of the two vaccines has achieved polio eradication in most of the world and the reported cases are due to the number of countries that have not vaccinated their entire population.

Clinical phases for a vaccine

Clinical phases are needed for the development of a vaccine, these are:

  • Preclinical trials. They are studies that are carried out in the laboratory (in vitro studies) and in animals (in vivo).
  • Phase I: trials  in healthy volunteers to study the tolerance and safety range of the vaccine. They are a small group between 20 and 100 volunteers. These are ADME studies. In pharmacology, the acronym  ADME comes  from  Absortión,  Distribution,  Metabolism  and  Excretion. It is used to describe how a pharmaceutical compound is processed in the body.
  • Phase II: trials in volunteer patients to determine efficacy in healing, side effects  and dosage. It involves the study of the candidate drug between 100 and 500 volunteer patients to determine the efficacy of the drug and its tolerance.
  • Phase III:  Trials on  a large number of patients for more information on efficacy in healing, side effects and dosage.
  • Phase IV:  compared to other drugs marketed.

At the moment there are a lot of companies that are working on finding the Sars-Cov-2 virus vaccine. On the next  page vaccine landcape,and with a last updated date of September 21, 2020,  there are 243 vaccine candidates and  43  are already in clinical trials.


The data on this page comes from,  a database of all the studies that are being conducted in the world at this time. For example, if we are looking for clinical studies from Spain you can see on this page:  clinicaltrials in Spain..

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Avelino Dominguez

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