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