Overview
- An international team identified adenovirus protein VII as the component that triggers antibodies cross‑reacting with platelet factor 4, causing TTS/VITT rather than the coronavirus antigen itself.
- The mechanism appears only in people with a particular immune‑gene variant combined with an exceptionally rare somatic hypermutation, accounting for the extremely low risk.
- The syndrome was associated with adenoviral vector vaccines from AstraZeneca and Johnson & Johnson and has not been observed with authorized mRNA vaccines.
- Both vector vaccines are no longer marketed in Europe, including the EU’s revocation of Vaxzevria’s authorization on 7 May 2024 after a request by AstraZeneca.
- Observed rates cited in reporting include about 1 in 200,000 after the Johnson & Johnson vaccine in the U.S. and roughly 3 in 100,000 after AstraZeneca in the U.K., and the study indicates modifying protein VII could avert future cases.