I believe it is an allergy to one of the ingredients in vaccines that can cause paralysis or even death. I know of two people locally who had flu shots and were paralyzed as a result, one of these being an in law of mine. He was extremely lucky though. After months of physical therapy and hard fighting, he managed to overcome it. He has never taken another one since. That is a horrible thing to risk when taking these shots. I have never taken one and will not ever.