April 21, 20216:18 PM UTC Healthcare & PharmaceuticalsExplainer: How worried should we be about links of blood clots to AstraZenecaâs vaccine? Ludwig BurgerJohn Miller 7 minutes read Syringes are prepared to administer the AstraZeneca coronavirus disease (COVID-19) vaccine at a new mass vaccination centre in WiZink sports arena in Madrid, Spain, April 9, 2021. REUTERS/Sergio Perez European regulators said the benefits of using Johnson & Johnsonâs (JNJ.N)and AstraZenecaâs(AZN.L) COVID-19 vaccines outweigh risks, even as they added warning labels to both shots for extremely rare but potentially fatal blood clotting. J&J said on April 20 it would resume deliveries of its vaccine in Europe, following the regulatorâs guidance. U.S. officials are continuing their review of what are now eight reported instances of rare clotting combined with low blood platelets in the United States.