I remember the fear and confusion of those early days when Gretchen Vogel and I were trying to make sense of the reports. And I have to say that reading a scientific paper has rarely given me the sense of satisfaction that this piece of scientific sleuthing did.
https://www.nejm.org/doi/full/10.1056/NEJMoa2514824

Five years after the rollout of Covid-19 vaccines started, it seems the mystery of why the Astra-Zeneca and J&J vaccines led to a rare but deadly side effect of unusual blood clots and bleeding has finally been solved. 

It's a fascinating case of molecular mimicry that may help make vaccine safer.

https://www.science.org/content/article/rare-dangerous-side-effects-some-covid-19-vaccines-explained