Paul Monagle Professor, Department of Paediatrics, The University of Melbourne The answer is usually a definitive “yes”. The blood clots we’ve seen following the AstraZeneca vaccine are completely different to other types of blood clots, such as deep vein thrombosis or a pulmonary embolism, or the clots that cause heart attacks and strokes. People with a history of these sorts of conditions don’t appear to be at any increased risk from the AstraZeneca vaccine. In fact, people in this group could be at greater risk from COVID-19, so shouldn’t delay getting vaccinated. First, how does blood form clots?