Assessing Case Fatality on Cases of Thrombosis with Concurrent Thrombocytopenia Following COVID-19 Vaccine AstraZeneca (Vaxzevria) in the United Kingdom: A Review of Spontaneously Reported Data

Introduction Thrombotic thrombocytopenia syndrome (TTS) events were reported very rarely following the coronavirus disease 2019 (COVID-19) vaccine AstraZeneca (Vaxzevria). Clinical and demographic characteristics of the affected people, including the outcomes of TTS events, need to be examined using available information to better understand aspects of this association. Objective To analyse clinical and demographic information of TTS events, including calculating the case fatality of reported cases of TTS by age and sex, using spontaneously reported data from the UK’s Yellow Card spontaneous reporting system of suspected adverse drug reactions. Methods TTS events reported to the Yellow Card scheme were extracted at weekly time points between 12 May 2021 and 25 May 2022. Cumulative numbers of TTS cases and deaths were recorded for each weekly interval, overall and stratified by age, sex, and vaccine dose. Results To 25 May 2022, 443 cases (81 fatal, 18.28%) had been reported in the UK. Events more frequently occurred following the first vaccine dose. No trends were observed for case fatality overall, or by age or sex. Conclusion In the UK, case fatality of TTS events reported to the Medicines and Health products Regulatory Agency (MHRA) following Vaxzevria has been approximately 17–18% since May 2021. There were no statistical differences in fatality based on age or sex. Most reports followed the first vaccine dose; none have been reported following a third dose to date, although Vaxzervia was not recommended for a third dose of COVID-19 vaccine in the UK. TTS remains very rare, and benefits of vaccination outweigh the risks.