Drug maker AstraZeneca has come under scrutiny for its COVID-19 vaccine. While it is not approved for use in the United States, reports connecting it to a small number of rare blood clots in Europe have raised concerns across the globe. “The safety concern is that there's been a very low incident of blood clots in patients that have received […] the AstraZeneca vaccine,” said University of Virginia infectious disease expert Dr. William Petri. “It's one specific kind of clot, which makes one concerned about whether that could be a side effect since it's not your everyday blood clot.”