Question Period Note: Adverse reactions & Vaccine safety

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• Safety is a central consideration for any health product, including vaccines. Canada’s rigorous regulatory system assesses vaccines for safety, efficacy and quality before they are authorized. However, no health product is completely risk-free.
• Post-market vaccine surveillance is required to monitor and understand how vaccines perform outside of clinical contexts and across large populations. Vaccine safety surveillance is critical for rapidly detecting and responding to safety issues, ensuring that the benefits of the vaccine continue to outweigh the risks and supporting vaccine uptake by building public confidence in Canada’s immunization programs.
• Safety and effectiveness are key considerations in Health Canada’s determination of which vaccines are fit to be authorized for use in Canada. These considerations are also weighed heavily in developing guidance on how and when these products should be used.
• Canada’s monitoring systems for adverse events following immunization rapidly detects possible safety issues and investigates them.
• Like any medication, vaccines can cause side effects and reactions, also known as adverse events. The benefits of vaccines authorized in Canada continue to outweigh their risks.
• As part of the Government’s continued commitment to openness and transparency, Health Canada and the Public Health Agency of Canada provide Canadians with monthly online updates on reported adverse events following immunization on Canada.ca.

Adverse events following immunization (AEFI)
An adverse event may occur after a person has been vaccinated. The majority of adverse events are expected mild reactions (e.g., pain, redness, swelling at the injection site, muscle soreness, mild headache), although serious and rare events can occur (e.g., allergic reaction). However, as the World Health Organization states: The fact that a vaccine was administered within a reasonable time period prior to the occurrence of an event does not automatically suggest that the vaccine caused or contributed to the event. Since medical events can occur throughout individuals’ lives, investigations are carried out to determine if a particular AEFI has a causal relationship to the administration of a vaccine.

Post-market COVID-19 vaccine safety monitoring
Post-market vaccine surveillance is required to monitor and understand how vaccines behave in the entire population and their real-world impact. Surveillance systems are used to identify changes in the frequency and/or severity of previously identified vaccine-related reactions (listed in the manufacturer monograph for the vaccine product) as well as to identify previously unknown adverse events following immunization that could be related to a vaccine. Vaccine safety surveillance is critical for rapidly detecting and responding to safety issues, ensuring that the benefits of the vaccine continue to outweigh the risks, and supporting vaccine uptake by building public confidence in Canada’s immunization programs.

Canada has a well-established vaccine safety surveillance system that is a collaboration between provinces and territories (P/T), the Public Health Agency of Canada (PHAC), Health Canada (HC), and vaccine manufacturers. Manufacturers are required to report serious adverse events to HC as the national regulatory authority, as well as submit regular summaries of global safety information. HC reviews these reports and takes appropriate regulatory actions should new safety issues be identified. In addition, PHAC receives and reviews reports of adverse events following immunization from federal, provincial and territorial (FPT) immunization programs through the Canadian Adverse Events Following Immunization Surveillance System. AEFI reports are continuously assessed and potential safety issues are flagged immediately for further investigation. This system has been enhanced to support the rollout of COVID-19 vaccines, to expedite the timeliness and sharing of information with partners and public reporting of adverse events. Those enhancements are being leveraged to monitor the use of the Imvamune vaccine in the current Monkeypox outbreak.

To enhance vaccine safety surveillance, the Government of Canada provides funding to: the Immunization Monitoring Program ACTive (IMPACT) network, a paediatric, hospital-based network that reports adverse events to PHAC; and to the Canadian Vaccine Safety (CANVAS) Network, a national web-based platform that collects information about health events occurring after COVID-19 vaccinations, and that provides regular reports to PHAC and P/T health authorities.

As of early August 2022, almost 90 million COVID-19 vaccine doses had been administered in Canada. It is notable that AEFIs were reported for 0.055% of all doses administered, and that only 0.012% of all reported AEFI were classified as serious (i.e. requiring hospitalization, life-threatening, and/or resulting in persistent or significant disability/incapacity or death).

PHAC and HC continue to closely monitor Canadian and international reports of the following safety signals:
• Thrombosis with thrombocytopenia syndrome following vaccination with the viral vector vaccine AstraZeneca Vaxzevria/COVISHIELD* COVID-19 vaccine. Health Canada has updated the product monograph to include information about these very rare events of blood clots associated with low levels of platelets following immunization.
• Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) following vaccination with COVID-19 mRNA vaccines. Data in Canada indicate a higher number of reports in younger people (i.e. less than 40 years of age) than would normally be expected in this age group in the general population. Health Canada updated the product monographs for both Moderna Spikevax and Pfizer-BioTech Comirnaty COVID-19 vaccines to include information around these risks.

Adverse Events of Special Interest (AESI) are pre-specified medically significant events that have the potential to be causally associated with a vaccine product. PHAC and HC continue to closely monitor various AESIs that have been identified domestically or internationally, such as appendicitis and unusual menstrual bleeding. Investigations (including research) are ongoing and emerging evidence will be communicated to Canadians as it becomes available.

• The COVISHIELD version of the AstraZeneca vaccine is no longer used in Canada as the interim order for its use expired on September 16, 2021.

• A robust vaccine safety surveillance system is essential for protecting the health and safety of Canadians, supporting public confidence in the safety of vaccines and strengthening Canada-wide immunization efforts.
• The Government of Canada continues to work closely with partners to monitor vaccine safety.