The 5W’s of adverse event reporting following immunization in Canada

By Yifan Zhou, Crystal Zhang, and Certina Ho

Everyone has a role in reporting adverse reactions to drugs and other health products. With the recent approval and mass distribution of COVID-19 vaccines, it is important to learn about the 5 W’s (Why, Who, What, When, and Where) of reporting adverse events following immunization (AEFI).

Why report?

Results of clinical trials provide us with a list of potential side effects associated with the drug product under development. However, the listed side effects may not be comprehensive or reflective in what may actually happen when the drug (e.g. the COVID-19 vaccine) is being administered to the general population.

Post-market adverse event reporting allows greater data collection from the general population for further safety profile analysis of the drug project that has been approved for use. This may help: (1) identify previously unknown adverse events; (2) understand an increase in adverse event frequency or severity; and (3) target areas requiring further investigation. The findings may then be used for updating the drug’s safety profile, product information, regulatory actions, and policy changes associated with provincial and/or federal initiatives.

Who can report?

Anyone can report a side effect to a vaccine at Reporters can be patients, health care providers, and drug manufacturers (Table 1).

What type of AEFI should be reported?

Any adverse event that is associated with vaccination should be reported even if the causal relationship has not been established. Adverse events that are serious, unexpected (regardless of seriousness), have a temporal association with vaccine administration, or have no other clear cause(s) at the time of reporting should be reported. Mild events, such as, transient injection site reactions, do not need to be reported. For further information, refer to the Reporting Adverse Events Following Immunization (AEFI) in Canada: User guide to completion and submission of the AEFI reports (

When/where to report?

If a patient experiences an AEFI, healthcare providers (HCPs) who provide immunizations should complete the AEFI form. Similarly, if patients experience adverse event(s) following immunization, they should ask their HCPs to complete the AEFI form accordingly. Note that the AEFI forms may differ between hospitals and provinces. The completed AEFI forms will be sent to local public health units, followed by federal/provincial/territorial immunization authorities, and ultimately to the Public Health Agency of Canada (PHAC), which, together with Health Canada, monitors vaccine safety in Canada (Table 1).


In the time of rapid and widespread immunization of COVID-19 vaccines, AEFI reporting ( is crucial to better understanding their safety profiles. Patients receiving vaccinations should be encouraged to reach out to their healthcare providers if they experience any adverse events. As COVID-19 vaccination providers, healthcare professionals play an important role in educating patients and contributing to ongoing vaccine safety monitoring.

Yifan Zhou and Crystal Zhang are PharmD Students at the Leslie Dan Faculty of Pharmacy, University of Toronto; and Certina Ho is an Assistant Professor at the Department of Psychiatry and Leslie Dan Faculty of Pharmacy, University of Toronto.


Table 1. Everyone Has a Role in Reporting Adverse Events Following Immunization (AEFI)



·         For the general public, the decision of reporting AEFI is voluntary. Patients can ask their HCPs to complete the AEFI form.

Health Care Providers (HCPs)

·         AEFI should be reported by HCPs as soon as possible, which will then be submitted to local public health units, federal/provincial/territorial immunization authorities, and PHAC, respectively.

·         Mandatory reporting of serious adverse drug reactions and medical device incidents by hospitals to Health Canada has been effective since December 16, 2019. Reporting is mandatory within 30 days.

Drug Manufacturers

·   They are required to report to Health Canada’s Canada Vigilance Program ( within 15 days of becoming aware of the adverse event.



·  This is an alliance of 12 pediatric centres across Canada. It actively screens for hospital admissions for neurologic events. If IMPACT identifies any unexplained adverse event temporally associated with an immunization, it will report to PHAC, federal/provincial/territorial immunization authorities, and local public health units for follow up.