Gretchen Vogel, Kai KupferschmidtScience’s COVID-19 reporting is supported by the Heising-Simons Foundation.The decision this week by more than 20 European countries to temporarily stop using AstraZeneca’s COVID-19 vaccine has opened a rift between vaccine safety experts, who say the cases of serious clotting and bleeding that triggered the pause are alarming and unusual, and public health officials concerned that the immunization pause on a continent in the grip of the pandemic’s third wave could take a heavy toll.“The harm caused by depriving people of access to a vaccine will likely vastly outweigh even the worst case scenario if any link to the clotting disorders is eventually found,” University of Leeds virologist Stephen Griffin told.