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Vaccine testing, approval, and monitoring

Date last reviewed: 
Thursday, Dec 21, 2023

How vaccines are tested

Vaccine testing begins in the laboratory. If lab studies show a vaccine has potential, it is usually tested in animals first. If the vaccine is safe in animals, clinical trials (studies with people) are next. People taking part in the clinical trials are volunteers. They understand that a vaccine is being studied and are informed about the possible side effects.
There are three phases of clinical trials. Phase one involves fewer than one hundred volunteers, phase two involves hundreds of volunteers, and phase three involves thousands.

Did you know?

Vaccines are among the most strictly regulated medical products in Canada. All vaccines go through an in-depth testing process and must be shown to be safe and effective before being approved for use in Canada. 

These trials provide very important information on:
  • Vaccine safety.
  • The immune response to the vaccine.
  • Vaccine efficacy (how well the vaccine prevents the disease.)
When all phases of the clinical trials have been successfully completed, the vaccine must meet Canadian licensing standards before it can be considered for approval by Health Canada.

Vaccine approval 

The Biologic and Radiopharmaceutical Drugs Directorate (BRDD), which is part of Health Canada, approves vaccines for use in Canada.
The BRDD approves a vaccine only if there is enough scientific evidence to show that it is safe, effective, and of suitable quality—and only if its benefits greatly outweigh any associated risks. 
The BRDD also supervises all aspects of vaccine production and quality control throughout the vaccine’s lifecycle to ensure that the vaccine is safe and effective.
A graphic demonstrating the steps and phases of pre-clinical studies, clinical studies and the final approval of vaccines.

Vaccine safety monitoring

Once a vaccine has been approved for use, its safety is continuously monitored. Ongoing vaccine safety monitoring is essential for the detection of and quick response to vaccine safety concerns.

The purpose of ongoing post-marketing vaccine safety monitoring is to detect possible adverse events that:

  • Occur at a higher frequency level than expected based on clinical trials or historical experience.
  • Occur very rarely, too rarely to detect even in a large clinical trial. When millions of people receive a vaccine, rare side effects may be recognized.

What is an adverse event?

An adverse event following immunization (also known as an AEFI) is any untoward (unexpected) medical occurrence after a vaccine has been given that may or may not have been caused by the vaccine.
By continually monitoring, we can know if there are changes in how often adverse events occur or if they occur only in certain groups of people.

How vaccine safety is monitored in Canada

Canada has several advanced systems (at the local, provincial, and national levels) to carefully monitor for adverse events and detect vaccine safety concerns.
By law in BC, a health care provider who suspects an AEFI must report the event to the medical health officer. Individuals (or their parents) are also advised to notify their immunization provider/clinic or health care provider about about any immunization-related concerns. Once reported, AEFIs are entered into BC’s electronic information system. Once an AEFI report is received, a local medical health officer or registered nurse reviews the report and makes a recommendation for future immunization. All AEFIs are reported to the BC Centre for Disease Control (BCCDC) for provincial surveillance and from there to the Public Health Agency of Canada for national surveillance and further assessment and investigation if needed.
The BCCDC receives and reviews all reports from around the province. By gathering all the reports in one place for the whole province, there is a greater opportunity to identify any safety signals and take action if appropriate. The Canadian Adverse Events Following Immunization Surveillance System (CAEFISS), part of the Public Health Agency of Canada, receives, tracks, and regularly analyzes reports from across the country to search for vaccine safety signals. With an even larger number of reports than at the provincial level, there is an even greater opportunity to identify any rare safety concerns.

Vaccine safety is also monitored at the international level. The World Health Organization’s International Drug Monitoring Program collects reports from over 75 countries (including Canada). It uses this global data set to monitor for any vaccine safety concerns.

Click here to view the graphic below in fullscreen.

A graphic demonstrating how vaccines are monitored at local, provincial, national and global levels.

Vaccine safety and the IMPACT surveillance system

Canada has a unique program called IMPACT that complements existing national surveillance systems. IMPACT is a pediatric hospital-based national active surveillance network for adverse events in children following immunization and selected infectious diseases that are, or will be, vaccine-preventable.
Nurse monitors are at 12 children’s hospitals across Canada (including BC Children’s Hospital). They review all admissions to the hospital for certain serious illnesses. If a child with any of these illnesses had recently received a vaccine, a report is sent to the local health unit and to the Public Health Agency of Canada to be investigated further. These events are reported even if another cause may ultimately be found for the illness.
The active nature of the surveillance ensures a high level of vigilance for severe AEFIs in children.

Mandatory reporting by vaccine manufacturers

Vaccine manufacturers are required to report serious or unexpected adverse events to the Canada Vigilance Program, as mandated by the Food and Drugs Act and Regulations. The Canada Vigilance Program is Health Canada’s post-market surveillance program that monitors the safety profile of health products once marketed to ensure that the benefits of the products continue to outweigh the risks.

Vaccine Vigilance Working Group (VVWG)

The VVWG was created in 2004 as part of the National Immunization Strategy to strengthen vaccine safety in Canada. It includes representatives from all federal and provincial/territorial immunization programs, as well as Health Canada regulators and IMPACT.
The group’s activities include providing a national vaccine safety sentinel network to rapidly share and disseminate information regarding vaccine safety issues or signals to appropriate stakeholders.


It’s often difficult to determine if an adverse event was caused by the vaccine or something else that happened around the same time the vaccine was given — for example, an infection or onset of a chronic condition that would have occurred even if the person had not been immunized. As a result, the details of all AEFI reports are carefully reviewed. Rates of adverse events in immunized people are compared to those of the same in people who are not immunized. This can help determine if the vaccine has a true safety concern. Some types of events are further investigated to clarify the cause. For instance, people with allergic reactions may be tested to find out which vaccine component caused the reaction.


Vaccine Safety in Canada