The vaccine produces spike protein and some research suggests that the spike protein itself is the source of vascular system damage. There was a contention that the vaccine spike protein is designed to stay on the surface of infected cells and not freely circulate into the bloodstream in large quantities but we also just don’t know for certain. It could even have to do with how the vaccine is administered and whether it largely affects the lymph system or a large quantity makes its way into the bloodstream.

https://www.salk.edu/news-release/the-novel-coronavirus-spik...