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. Prof. Greinacher and his team has just begun examining Johnson & Johnson’s vaccine but has identified more than 1,000 proteins in AstraZeneca’s vaccine derived from human cells, as well as a preservative known as ethylenediaminetetraacetic acid, or EDTA. Their hypothesis is that EDTA, which is common to drugs and other products, helps those proteins stray into the bloodstream, where they bind to a blood component called platelet factor 4, or PF4, forming complexes that activate the production of antibodies. The inflammation caused by the vaccines, combined with the PF4 complexes, could trick the immune system into believing the body had been infected by bacteria, triggering an archaic defense mechanism that then runs out of control and causes clotting and bleeding.