EMA workshop on thrombosis with thrombocytopenia syndrome
EventHumanCOVID-19
Date
- Monday, 27 June 2022
Location
- OnlineEuropean Medicines Agency, Amsterdam, the Netherlands
On 27 June 2022, the European Medicines Agency (EMA) hosted a virtual workshop to review the current understanding of the pathophysiology of thrombosis with thrombocytopenia syndrome (TTS), an extremely rare but serious adverse event that can occur after immunisation with an adenovirus-based COVID-19 vaccine, and to discuss next steps in the research agenda.
International regulators, academic researchers as well as the marketing authorisation holders for the two approved adenovirus-based COVID-19 vaccines in the EU shared the available data generated so far and participated in the discussion. The meeting was divided into four sessions:
- Session 1. Pharmacoepidemiology: Population-based studies of vaccine-induced TTS
- Session 2. Clinical characterisation of TTS
- Session 3. Understanding the biological mechanisms and impact of vaccine composition on TTS
- Session 4. Agreement on research agenda and future directions
Cases of TTS or vaccine-induced immune thrombotic thrombocytopenia (VITT) have been mainly reported in Europe, North America and Australia. However, in other countries, where these vaccines are widely used, there are no significant reports of this side effect. The group highlighted the need to improve surveillance activities in low- and middle-income countries and to contribute to the creation of supporting testing and surveillance networks
The workshop participants reiterated that the presence of antibodies to a protein released from platelets, called platelet factor 4 (PF4), is a key feature of cases of thrombosis and thrombocytopenia after vaccination with an adenovirus-based COVID-19 vaccine. This should not be confused with other cases of TTS that have a different pathophysiology and are not associated with vaccination.
The participants also discussed the current of play of research on the interaction between PF4 and the vaccine adenovector capsids. Comparing results from studies using different methodologies, the participants agreed that despite the tremendous amount of scientific work done so far, some aspects require additional investigation. This includes in particular: better characterising the immune responses in people who have developed TTS; analysis of potential genetic factors involved; characterisation of (co-)factors contributing to the pro-inflammatory milieu potentially involved in triggering TTS.
A document summarising the key aspects and the agreed steps forward will be published in due time.