Public Health Ontario

Adverse Events of Special Interest (AESIs) for COVID-19 Vaccines Surveillance

Following the authorization of novel Coronavirus Disease 2019 (COVID-19) vaccines in Canada, post- marketing surveillance is being conducted to monitor the safety of these new vaccines throughout the implementation of the immunization program. Provincial reporting of adverse events following immunization (AEFIs) to Canada’s AEFI Surveillance System (CAEFISS) is an important component of post- marketing surveillance in Canada.

An AEFI is defined as any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the use of a vaccine. Reporting of adverse events of special interest (AESIs) for COVID-19 vaccines in the context of overall AEFI surveillance enables enhanced monitoring by pre-specifying events which may otherwise not be captured or readily analyzed from a passive surveillance system. In addition to AESIs identified before the launch of COVID-19 vaccine programs, this document outlines guidance for the reporting of events identified through post-marketing surveillance and continues to be the focus of enhanced monitoring (e.g., thrombosis with thrombocytopenia syndrome (TTS) following viral vector vaccines and myocarditis/pericarditis following mRNA vaccines).