Persistent questions on whether rare but serious blood clots among those getting the AstraZeneca jab against Covid-19 are more frequent than in the general population, and what causes them if they are, have continued to undermine confidence in the beleaguered vaccine. The European Medicines Agency--which has said that benefits outweigh risks such that the vaccine should remain in use--will provide an updated assessment next week. What serious events have been reported? The blood clots seen in a handful of people vaccinated with AstraZeneca are described by the French Medicines Agency (ANSM) as