Advisory Committee on Causality Assessment

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The Advisory Committee on Causality Assessment (ACCA) is part of Canada’s vaccine safety surveillance system. This committee of experts reviews reports of adverse events following immunization (AEFI). It determines whether an event was likely to have been causally related to a given vaccine.

ACCA membership includes Public Health Agency of Canada (PHAC) and Health Canada physician experts in causality assessment. Additional specialized medical expertise is sought externally when required to:

When someone experiences an adverse event (side effect) after being vaccinated, the provincial or territorial health authority reports it to PHAC. The reports are compiled into the Canadian Adverse Events Following Immunization Surveillance System database.

Similarly, the Canada Vigilance Program, managed by Health Canada, receives adverse event reports from:

ACCA uses scientific evidence and medical expertise to investigate if serious events are related to a vaccine.

Learn more about:

Vaccine safety monitoring

PHAC and Health Canada monitor the safety of all vaccines approved in Canada to confirm that their benefits continue to outweigh any risks.

If a safety issue is identified, appropriate actions can be taken, such as:

Investigating serious adverse events

ACCA assesses serious events after vaccination to determine the likelihood that they’re vaccine related or not. The committee uses a process based on a standardized procedure developed by the World Health Organization. Such processes have a long history of use. They’re also used in drug safety monitoring and by other international regulatory and public health authorities.

When an adverse event occurs after vaccination, it doesn’t necessarily mean that the vaccine caused the adverse event. It may have been caused by other factors. Some medical events occur coincidentally in the hours, days or weeks after vaccination, and are unrelated to the vaccine. This is seen particularly when millions of people are being vaccinated.

ACCA assesses reports of serious adverse events to determine the likelihood that the event was caused by the vaccine. Medical experts conduct a medical review and a critical evaluation of the scientific evidence. They consider many different factors, and the likelihood that any of those factors might have contributed to the adverse event, even if the person hadn’t received a vaccine. These factors could include but are not limited to age, sex, pre-existing medical conditions or a recent illness that may have increased the person’s risk for the adverse event.

Causality assessment

A causality assessment is a critical part of vaccine safety monitoring. It’s a standardized review of an adverse event following vaccination to determine whether or not a causal association between the event and the vaccine is likely.

Causality assessments are often challenging. There is a broad range of evidence that is brought together for the causality assessment. For example, a positive functional test (anti-PF4 antibodies) can indicate a case of thrombosis with thrombocytopenia syndrome following vaccination with a viral vector COVID-19 vaccine. This, combined with imaging results and other clinical evidence, can help to establish the relationship with the vaccine. Cases involving similar adverse events are assessed as a group. This makes causality assessment a later step in the process of vaccine safety monitoring.

In some cases, there may not be enough evidence for ACCA to determine if there’s a causal relationship between the vaccine and the adverse event. ACCA’s assessment may be limited by the amount and level of detail in the information available at the time of the assessment.

For more information, refer to the World Health Organization’s causality assessment.

Available assessments


Provincial and territorial health authorities remove directly identifying information when they submit case reports to PHAC. This includes name, address and other potentially directly identifying information not needed for the assessment.

Reports contain only the medical information relevant to the adverse event. All information is kept strictly confidential at all times.

Vaccine Injury Support Program

The Vaccine Injury Support Program (VISP) provides financial support for people who experience a serious and permanent injury as a result of receiving a Health Canada-authorized vaccine, administered in Canada, on or after December 8, 2020. The VISP is administered by an independent third party.

VISP and ACCA are independent from one another. Both use the standardized, internationally accepted method for determining causality developed by the World Health Organization. However, the processes used to obtain medical information and the objectives are different. There is no information shared between ACCA and VISP.

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