I was reading that the spike protein is similar to proteins found in many tissues, and once you get exposed to the real virus you body can start attacking itself (cytokine storm or something like that).

Previous corona vaccine trials were abandoned because in animals they would be fine after the vaccine but later when exposed to the virus in the wild would die or suffer very negative outcomes worse than the disease itself. I think we understand better now why that was happening.

Note that these problems with coronavirus vaccines were never overcome... good look to all of the vaccine test subjects when they start getting exposed to corona in the wild. If we have an uptick in deaths it'll probably be blamed on a new variant, but anyone with half a brain will be able to tie it back to these rushed through vaccines.