The Institute of Medicine released a report which details their study on vaccines and possible side effects. From their website comes this statement - verbatim:
Using epidemiologic and mechanistic evidence, the committee developed 158 causality conclusions and assigned each relationship between a vaccine and an adverse health problem to one of four categories of causation:
- Evidence convincingly supports a causal relationship
- Evidence favors acceptance of a causal relationship
- Evidence favors rejection of a causal relationship
- Evidence is inadequate to accept or reject a causal relationship
The IOM also created a chart which I find very helpful. You can view it by clicking this link. It does take a while for this link to open so be patient with it.
To learn even more about the committee research and vaccine safety please go to the website and access the full report, which you can do here.