Map of Simcoe Muskoka


Vaccine Safety

Immunization is arguably the most effective, lowest cost and safest intervention to improve health in the past century. In Simcoe Muskoka in 2010, the vast majority of parents of school children (5 to 17 years old) strongly or somewhat agreed that immunizing children protects them from disease (97% +/- 2%) and that vaccines are safe for children to have (92% +/- 3%) (RRFSS).

Monitoring Vaccine Side Effects:

While vaccines are very safe, occasionally side effects do occur.  All possible side effects after immunization, called ‘adverse events’, are taken seriously and closely monitored. An adverse event is any unwanted medical reaction following immunization, whether it is related to the vaccine or not. In Canada, the Canadian Adverse Events Following Immunization Surveillance System (CAEFISS) and the Immunization Monitoring Program ACTive (IMPACT) monitor adverse events after immunization.

The Ontario Health Protection and Promotion Act requires health care providers to report adverse events following immunization to the health unit. In Simcoe Muskoka in a typical year, there are approximately 10 adverse events following immunization among the hundreds of thousands of vaccines administered by the health unit and distributed to health care providers (iPHIS, BIOS). Among these cases, the most commonly reported symptoms are localized swelling, red arm, and mild fever (less than 38 degrees Celsius). There have been no deaths (iPHIS).

The risks associated with vaccines are many times lower than the consequences of the diseases they prevent. Some people get a mild fever or soreness at the injection site. These reactions can be part of the body’s normal response to the vaccine and do not usually last long. Approximately one person in every one million doses of vaccine distributed experiences a severe allergic reaction called anaphylaxis. This reaction can be effectively treated by the nurse or doctor administering the vaccine. The questions that patients are asked before getting a vaccine are designed to screen out the people at highest risk of severe reactions.

For more information on vaccine safety, see one of the following credible sources:

Public Health Agency of Canada’s Frequently Asked Questions at

Ontario Ministry of Health and Long Term Care at

Simcoe Muskoka District Health Unit at

Cause and Effect

The key to understanding vaccine safety is understanding that just because adverse events occur after immunization does NOT mean they were necessarily caused by the immunization.

In order to determine whether adverse events are caused by immunization, researchers conduct large studies called clinical trials. These studies only occur after the vaccine has been proven safe in multiple stages of testing by the Biologics, Radiopharmaceuticals and Genetic Therapies division of Health Canada. Researchers recruit thousands of participants and divide them into two groups: one group receives the vaccine and the other group receives a placebo (e.g. a shot of salt water). If the adverse events occur equally in both groups, then the vaccine is not the cause because people who did not receive a vaccine are experiencing the same events. Only by comparing the two groups can researchers make any conclusions. Vaccines must be proven safe in large clinical trials before being licensed for public use.