Together with colleagues from across Canada, the United States, Brazil, Finland and Australia, she decided to look at unusual cases without specific known causes that tend to be attributed to vaccines. Background information was gathered about health conditions such as Guillain-Barre syndrome, Multiple Sclerosis and spontaneous abortions. The researchers also looked at cases of sudden unexplained death. These incidents are so uncommon that they are detected only when very large groups are studied.

As a result, they're able to identify the rate that these conditions occur in a given population when there is no ongoing vaccine campaign - the 'coincident background cases.' With this new information, public health officials will be able to monitor reported cases of adverse reactions following a vaccination program and see if rates jump or stay the same.

The report's authors are primarily hoping to reach health care policy and decision makers with their findings.

"I think the public can be reassured that there is careful thought and evaluation of any adverse event that occurs around vaccination programs. All incidents are taken very seriously and great care is taken in the follow up assessments," says Dr. MacDonald.

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