The Canadian Adverse Events Following Immunization Surveillance System (CAEFISS) is a national reporting system for vaccine safety that is monitored by the Centre for Immunization and Respiratory Infectious Diseases. CAEFISS allows coordinated and centralized monitoring of possible adverse events (possible side effects) that occur after the administration of Canadian-licensed vaccines.

If a reaction occurs after a vaccination, health professionals may report it to the (CAEFISS), regardless of whether the symptoms are thought to be related to the vaccine. Just because a reaction was reported to CAEFISS does not mean the vaccine caused the reaction. Careful studies are conducted if a pattern emerges that suggests potential problems with a vaccine.