Expert says he found why some COVID-19 vaccines trigger clot issues

Scientists world-wide are racing to understand why Covid-19 vaccines from AstraZeneca PLC and Johnson & Johnson are causing rare but potentially deadly blood clots.

"Understanding the cause is of highest importance for the next-generation vaccines, because [the novel] coronavirus will stay with us and vaccination will likely become seasonal," said Eric van Gorp, a professor at Erasmus University in the Netherlands who heads a group of scientists studying the condition. In Germany, one researcher thinks he has found what is triggering the clots. Andreas Greinacher, a blood expert, and his team at the University of Greifswald believe so-called viral vector vaccines—which use modified harmless cold viruses, known as adenoviruses, to convey genetic material into vaccine recipients to fight the coronavirus—could cause an autoimmune response that leads to blood clots. According to Prof. Greinacher, that reaction could be tied to stray proteins and a preservative he has found in the AstraZeneca vaccine.