Link between AstraZeneca vaccine and blood clots clear: EMA official By IANS | 5 Views Denmark halts use of AstraZeneca vaccine over concerns of blood clots.. Image Source: IANS News Rome, April 7 : There is a causal link between the coronavirus vaccine developed by AstraZeneca and very rare cases of blood clots, although it remains unclear what the connection is and the possible causes are likewise still unknown, a senior European Medicines Agency (EMA) expert told an Italian on Tuesday. "It is clear that an association exists" between the vaccine and the dozens of reported blood clots, said Marco Cavaleri, head of the EMA's health threats and vaccines strategy.