A study in mice found that the condition occurred with some frequency when the vaccine was administered intravenously. So, possibly inadvertent injection into a

A study in mice found that the condition occurred with some frequency when the vaccine was administered intravenously. So, possibly inadvertent injection into a vein, causing mRNA to be taken up by heart muscle cells which then express spike protein, and either the immune system attacks those cells or the cytotoxic nature of the spike itself kills them off. Aspirating the needles could help avoid this but the CDC explicitly says it is not necessary. https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciab707/6353927 https://academic.oup.com/cid/advance-article/doi/10.1093/cid...