Immune response may be linked to AstraZeneca vaccine clot issue Four previously healthy individuals who got the AstraZeneca shot and developed life-threatening clots Reuters April 01, 2021 Vials labelled "Astra Zeneca Covid-19 Coronavirus Vaccine" and a syringe are seen in front of a displayed AstraZeneca logo, in this illustration photo taken March 14, 2021. PHOTO: REUTERS The following is a roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for Covid-19, the illness caused by the virus. Immune response may explain rare clots after AstraZeneca vaccine Researchers may have found an explanation for the rare but serious blood clots reported among some people who received AstraZeneca's Covid-19 vaccine. They believe the phenomenon is similar to one that rarely occurs with a blood-thinning drug called heparin, called heparin-induced thrombocytopenia (HIT). In HIT, the drug triggers the immune system to produce antibodies that activate platelets, which cause blood to clot.