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Vaccine development process

Several steps are required to make a vaccine. Here is a summary of the steps:

1. Understand the disease

Recognizing and diagnosing the disease is the first step in the vaccine development process. In this step, the infectious agent (the virus or bacterium responsible for the disease) is identified. Studies are done to locate where the infectious agent is found in nature, how it is transmitted, how often it causes new cases, etc.

2. Understand the infectious agent

In this step, scientists study and try to understand the infectious agent, its biochemical properties, its ability to reproduce artificially, and analyze its genetic material (genes and antigens). They also study the immune defence mechanisms of the human body against this infectious agent. Based on this information, an animal species is identified to test the different versions of the vaccine on. It is selected based on its immune response to the infectious agent, which must be as close as possible to that of humans.

3. Conduct preclinical studies in animals

Scientists must then find a way to make the infectious agent harmless. The infectious agent is weakened, killed or divided into small portions to deprive it of its ability to transmit diseases. Then, a protein or sugar on the surface of the infectious agent, also known as an antigen, is selected. It is these antigens that will be recognized by the immune system and trigger the production of antibodies. Other substances may be added to the vaccine to extend its shelf life, improve its efficacy or facilitate its administration. To learn more about what goes into a vaccine, see Vaccine ingredients.

Preclinical studies also include the manufacture of different versions of the vaccine so that several doses and variations can be tested. The different versions produced are tested on the selected animal species. Among other things, antibody production in the animal and adverse reactions are documented. The version of the vaccine that gave the best results and is best tolerated is selected and then a few hundred doses are produced.

4. Conduct clinical studies in humans

Phase I

In this phase, the new vaccine is given to a small number of healthy volunteers, usually between 10 and 100 people. The goal of this phase is to assess the immune response and the safety of the vaccine in humans.

Phase II

The vaccine is given to more healthy volunteers, usually between 50 and 500 people. Phase II confirms the safety and efficacy of the vaccine, but it primarily determines the vaccination schedule and the number of doses required to protect the person from the disease.

Phase III

The goal of this phase is to determine whether the vaccine is safe and effective in preventing disease in a large number of people. The vaccine is given to several thousand people. People are selected from the target vaccination group.

5. Get the vaccine approved

Approval is the process of verifying that a vaccine meets the standards and recommendations of the country in which it will be administered. It ensures that it is compliant and safe. Any new vaccine must be approved by a recognized organization before it can be distributed. Each lot of a vaccine undergoes safety testing. Health Canada is the agency responsible for approving vaccines in Canada.

6. Produce and market the vaccine

The vaccine is produced in large quantities so that it can meet demand and be marketed.

7. Document vaccine safety and efficacy

Once large-scale vaccination has begun, efficacy in the field and post-vaccination symptoms must be documented. This step is called Phase IV and is when post-marketing studies are done.

8. Add the vaccine to immunization programs

Vaccine approval does not necessarily mean that it will be used in a free public immunization program. This type of program must have public health objectives, that is, the eradication, elimination or control of a disease, and provide strategies to achieve them.

Public health objective



Permanent disappearance of an infectious disease worldwide.


The disease can be transmitted, but does not cause epidemics.


Reduced mortality, hospitalizations or complications associated with a disease.

To be able to make an informed decision regarding the addition of a vaccine to the Québec Immunization Program, Québec experts, the Comité sur l’immunisation du Québec and the Ministère de la Santé et des Services sociaux use the following criteria:

  • Burden of the disease on society: severity, consequences, frequency, affected groups, alternative prevention, availability of treatment and socioeconomic impact.
  • Vaccine safety and efficacy.
  • Program objectives and immunization strategy to achieve them.
  • Availability of funds and comparability with other interventions:
  • cost effectiveness
  • Vaccine demand or acceptability by the population and health care professionals.
  • Feasibility of implementation: availability of resources and funds.
  • Ability to evaluate the program.
  • Fairness of the program: accessibility.
  • Compliance of the program with those implemented elsewhere.
  • Ethical, legal and political considerations.

Vaccines introduced in Québec since 2000 have been analyzed against these criteria. For more information, go to the page Maladies infectieuses This hyperlink will open in a new window. [Infectious diseases; French only] on the website of the Institut national de santé publique du Québec.

Explainer video

See also the COVID‑19: How vaccines are developed This hyperlink will open in a new window. video on Canada.ca to know the steps required to make a vaccine.

Last update: December 16, 2020


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