COVID vaccination: we now may know why some people developed blood clots

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Richard Buka and Samantha Montague

COVID vaccines saved millions of lives, but months into the rollout, a small number of people began developing dangerous blood clots in unusual parts of the body. These only happened after vaccines that used a modified adenovirus to deliver its payload – such as the AstraZeneca vaccine. Why these blood clots formed was a mystery – until now.

The condition was named vaccine-induced immune thrombocytopenia and thrombosis, or VITT. It happens when the immune system mistakenly attacks one of the body’s own proteins, called platelet factor 4.