Its an acute issue that is rare. In this case, its rarer than the normal rate from getting COVID isn't it? The chance of catching COVID is high, not low, without the vaccine. The vaccine does not guarantee protection in the sense that no vaccine does, but thus far it appears to work at least as well or better than any other vaccine. For the health issues, most of your same concerns apply to COVID which by definition carries at _least_ as much risk as the vaccine given its modus operandi. For the symptom in question the risk appears to be lower -- by a LOT -- than if people were to get the virus naturally. Its only being reported at all because the monitoring is good -- did you look at how few cases and the deviation they detected? Its on the order of normal: 100, now: 200, amongs _millions_ of vaccine doses. And presumably that's _after_ they rule out COVID. Per your "not guaranteed protection" line of reasoning, these cases might not even be from the vaccine in the first place, but from people who got COVID right around the same time. I can understand apprehension about new medicine.