Adverse events following immunization in Canada: Understanding the data

Data source

Data for this dashboard come from the Canadian Adverse Events Following Immunization Surveillance System (CAEFISS), which is managed by the Public Health Agency of Canada (PHAC). Reports of AEFIs are submitted to CAEFISS by provincial and territorial health authorities. AEFI reports received by National Defence are reported directly to PHAC. AEFI reports from active surveillance in pediatric hospitals are also reported to CAEFISS. All reports in CAEFISS are coded using MedDRA (Medical Dictionary for Regulatory Activities) terminology.

CAEFISS is a dynamic database, meaning new reports may be submitted for previous years, and existing reports can be updated with new information or corrections. This dashboard data is accurate to the time it was extracted and may differ from other publications.

Learn more about data collection in How vaccine safety is monitored.

Definitions

Adverse Event Following Immunization (AEFI)

An AEFI is any untoward medical occurrence that follows immunization. It is not necessarily caused by the vaccine. The adverse event may be any:

• unfavourable or unintended sign, for example, skin rash
• abnormal laboratory finding
• symptom
• disease

One adverse event report represents one person. The report may include more than one symptom, sign or other health event, as in the list above. Each event is considered an AEFI.

Canadian Immunization Guide: Part 2. Vaccine safety

Serious adverse event reports

An event is considered serious if it:

• results in death
• is life-threatening, an event or reaction in which the patient was at real, rather than hypothetical, risk of death at the time of the event or reaction
• requires in-patient hospitalization or prolongation of existing hospitalization
• results in persistent or significant disability or incapacity
• results in a congenital anomaly or birth defect

Canadian Immunization Guide: Part 2. Vaccine Safety

Safety signal

A safety signal is information from one or more sources that can include AEFI reports that suggests a new and potentially causal association between a vaccine and a medical event. The event could be unknown or incompletely documented, or the event could be a new aspect of a known association. The primary purpose of post-market vaccine safety surveillance is to detect such safety concerns.

For more information, refer to the World Health Organization’s Global Manual on surveillance of adverse events following immunization.

Vaccine doses distributed

Data for the number of doses distributed in Canada in 2024 were reported directly to PHAC by vaccine manufacturers or distributors. Only the yearly total number of vaccine doses distributed in Canada is currently available. Information may be missing or incomplete for certain vaccines.

The number of doses distributed is not the same as the number of people vaccinated. Not all doses distributed are administered as there may be some wastage and returns of unused doses. Some vaccines require more than one dose for an individual to be considered fully vaccinated.

Interpretation

An AEFI report indicates that a health event occurred after vaccination and was reported to public health. A report does not mean the vaccine caused the event. Some reports, especially serious, unusual or unexpected events, may be reviewed in more detail, including through causality assessment and signal investigations.

Trends in reporting adverse events can be influenced by various factors, including:

• public awareness
• new immunization programs or large immunization campaigns, such as for COVID-19
• changes to immunization programs and guidance
• shifts in AEFI surveillance practices over time, such as case definitions, reporting guidelines or data collection methods

Healthcare providers are required under most provincial and territorial public health legislation to report adverse events following immunization. They must do so whether or not they are certain that the vaccine was the cause.

Age group and sex

Reports may have unknown or missing age and/or sex because individuals chose not to give this information, or it was not known at the time of reporting. Due to small numbers, reports with undisclosed age or sex are excluded from the analysis by age and sex. These reports are still included in the overall totals.

Differences by sex should be interpreted with caution. They may reflect differences in vaccination rates or healthcare-seeking and reporting behaviour rather than true biological differences. Reporting may vary by age, sex and year due to many factors, such as:

• changes to vaccine programs and schedules
• large-scale vaccination campaigns
• shifts in awareness
• healthcare seeking and access
• AEFI reporting practices

These factors are especially relevant to the COVID-19 mass vaccination campaign (2021–2022).

Vaccines and vaccine groupings

Vaccines are grouped into categories based on their primary recommendations for use in Canada, such as the typical age groups or situations when they are administered.

The groupings are:

• infant and childhood vaccines typically given to children under 12 years old
• adolescent vaccines typically given to individuals 12 to 17 years old
• adult vaccines typically given to adults 18 years and older
• influenza vaccines, recommended every year
• pneumococcal vaccines, recommended for children and older adults
• travel vaccines
• COVID-19 vaccines, recommended every year, especially for older adults

The Canadian Immunization Guide provides national recommendations, but immunization programs and schedules may vary by province or territory. The National Advisory Committee on Immunization recommendations may have some flexibility, such as by age range and risk factors.

Learn more about provincial and territorial immunization programs for infants and children and previously immunized adults.

Limitations

The majority of reports received in CAEFISS come from voluntary reporting by healthcare providers and the public. Most provinces and territories, however, require healthcare providers to report certain events that come to their attention. Therefore, adverse event reporting to CAEFISS may be limited by:

• underreporting, where not all events that occur are reported
• reporting delays across jurisdictions and levels of public health, from local to provincial or territorial and then to CAEFISS
• missing or incomplete information provided in a case report, such as underlying medical conditions or medications, which limits analysis

Reports may contain information that is partial, uncertain, coincidental, or not clinically confirmed.

More information on vaccine safety monitoring

• Canadian Adverse Events Following Immunization Surveillance System (CAEFISS)
  • Adverse events following immunization (AEFI) reporting form
• Vaccine safety in Canada
• Vaccination coverage in Canada
• Canadian Immunization Guide
  • Part 2 Vaccine Safety
• Canada Vigilance Program