After weeks of investigation, the European Medicines Agency (EMA) announced on 7 April that there is a possible link between the clots and the vaccine. The clots also appeared in unusual parts of the body, such as the brain and abdomen, rather than in the legs, where most deep-vein blood clots form. Heparin is normally used to prevent clotting, but in very rare cases can trigger a syndrome called heparin-induced thrombocytopenia (HIT), which causes blood clots together with low platelet levels. The team will look for potential cases of HIT among cases of blood clots following vaccination with the Oxford–AstraZeneca vaccine and other COVID-19 vaccines. “We tested her blood and found reactions exactly the same as reported for the AstraZeneca reactions,” he says.