There have been studies on the risks you mentioned for years now. It was studies done by the scientific community and the changes in protocol made that is how we know about it at all. Do you think the conspiracy theorists figured it out and scientists went "oh we should study this thing the flat earthers all keep saying about our vaccines"... lol... nah, the scientists found it on their own, announced it, did studies, changed protocols, all on a very very low risk event out of an abundance of caution.. then the conspiracy theoriests took it and went "seeeeeeeeeee its not safe after all!".