Beginning in February, 2021, multiple European countries (e.g., Austria, Denmark, Norway, Germany, UK) and Australia have reported cases of thrombosis with thrombocytopenia syndrome (TTS) in persons who received the Astra-Zeneca (AZ) COVID-19 vaccine (1-3, 10) and more recently in the US with the Janssen vaccine (11). In May 2021, a draft interim case definition was proposed by the Brighton Collaboration. Since that time, understanding of this condition and its relationship to vaccines has evolved. Recent work by Andreas Greinacher and others now allow revision of the original case definition and level of certainty algorithm.1 The goal of this case definition is to facilitate harmonized studies of this outcome. This supplements guidelines published by WHO provided information on case identification for treatment.

The SPEAC Projec is funded in whole by CEPI.