EXPLAINER-How worried should we be about blood clots linked to Astra, J&J vaccines? Reuters 1 hr ago (Adds details following EMA warning label for J&J vaccine) By John Miller and Ludwig Burger ZURICH, April 21 (Reuters) - European regulators said the benefits of using Johnson & Johnson's and AstraZeneca's 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 regulator's 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.