Global Advisory Committee on Vaccine Safety (GACVS) review of latest evidence of rare adverse blood coagulation events with AstraZeneca COVID-19 Vaccine (Vaxzevria and Covishield)

"A very rare new type of adverse event called Thrombosis with Thrombocytopenia Syndrome (TTS), involving unusual and severe blood clotting events associated with low platelet counts, has been reported after vaccination with COVID-19 Vaccines Vaxzevria and Covishield... 

Thrombosis in specific sites (such as the brain and abdomen) appears to be a key feature of TTS. Clinicians should be alert to any new, severe, persistent headache or other significant symptoms, such as severe abdominal pain and shortness of breath, with an onset between 4 to 20 days after adenovirus vectored COVID-19 vaccination."