The safety committee of the European Medicines Agency (EMA) has found that the Oxford-AstraZeneca Covid-19 vaccine can cause unusual blood clots with low blood platelets, but stresses the overall benefits of the vaccine in preventing coronavirus outweigh the risks of side effects.The safety committee of the European Medicines Agency (EMA) has found that the Oxford-AstraZeneca Covid-19 vaccine can cause unusual blood clots with low blood platelets, but stresses the overall benefits of the vaccine in preventing coronavirus outweigh the risks of side effects.