Embolic and thrombotic events after COVID-19 vaccination

"VITT" redirects here. For other uses, see VITT (disambiguation).

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Post-vaccination embolic and thrombotic events, termed vaccine-induced immune thrombotic thrombocytopenia (VITT),[1][2][3][4][5] vaccine-induced prothrombotic immune thrombocytopenia (VIPIT),[6] thrombosis with thrombocytopenia syndrome (TTS),[7][4][5] vaccine-induced immune thrombocytopenia and thrombosis (VITT),[5] or vaccine-associated thrombotic thrombocytopenia (VATT),[5] are rare types of blood clotting syndromes that were initially observed in a number of people who had previously received the Oxford–AstraZeneca COVID‑19 vaccine (AZD1222)[a] during the COVID‑19 pandemic.[6][12] It was subsequently also described in the Janssen COVID‑19 vaccine (Johnson & Johnson), leading to the suspension of its use until its safety had been reassessed.[13] On 5 May 2022 the FDA posted a bulletin limiting the use of the Janssen Vaccine to very specific cases due to further reassessment of the risks of TTS, although the FDA also stated in the same bulletin that the benefits of the vaccine outweigh the risks.[14]

In April 2021, AstraZeneca and the European Medicines Agency (EMA) updated their information for healthcare professionals about AZD1222, saying it is "considered plausible" that there is a causal relationship between the vaccination and the occurrence of thrombosis in combination with thrombocytopenia and that, "although such adverse reactions are very rare, they exceeded what would be expected in the general population".[12][15][16][17] AstraZeneca initially denied the link, saying "we do not accept that TTS is caused by the vaccine at a generic level". However, in legal documents filed in February 2024, AstraZeneca finally admitted its vaccine 'can, in very rare cases, cause TTS'.[18][19]

  1. ^ Cite error: The named reference GreinacherNEJM was invoked but never defined (see the help page).
  2. ^ Cines DB, Bussel JB (June 2021). "SARS-CoV-2 Vaccine-Induced Immune Thrombotic Thrombocytopenia". The New England Journal of Medicine. 384 (23): 2254–2256. doi:10.1056/NEJMe2106315. PMC 8063912. PMID 33861524.
  3. ^ Liu Y, Shao Z, Wang H (December 2021). "SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia". Thrombosis Research. 209: 75–79. doi:10.1016/j.thromres.2021.12.002. PMC 8647389. PMID 34894531.
  4. ^ a b Klok FA, Pai M, Huisman MV, Makris M (November 2021). "Vaccine-induced immune thrombotic thrombocytopenia". The Lancet. Haematology. 9 (1): e73–e80. doi:10.1016/S2352-3026(21)00306-9. PMC 8585488. PMID 34774202. Although initially several terms were used to describe the syndrome … the term that has gained widespread use is vaccine-induced immune thrombotic thrombocytopenia (VITT). Thrombosis with thrombocytopenia syndrome has also been used, but it is a more general term that can be caused by other conditions
  5. ^ a b c d Warkentin TE, Pai M (October 2021). "Editorial on Thaler et al. long-term follow-up after successful treatment of vaccine-induced prothrombotic immune thrombocytopenia. Thromb Res 2021 in press". Thrombosis Research. 207: 158–160. doi:10.1016/j.thromres.2021.10.007. PMID 34757250. S2CID 239574011. We believe the name "VITT" works well … the term clearly denotes the key features of the disorder … provides a useful mnemonic for disease recognition in the usual sequence of events … need not mandate that thrombosis be present … "TTS" … has limited clinical utility, since many conditions … present with the duad of thrombosis and thrombocytopenia
  6. ^ a b "Use of AstraZeneca COVID-19 vaccine in younger adults" (Press release). Health Canada. 29 March 2021. Archived from the original on 11 October 2021. Retrieved 2 April 2021.
  7. ^ Long B, Bridwell R, Gottlieb M (November 2021). "Thrombosis with thrombocytopenia syndrome associated with COVID-19 vaccines". The American Journal of Emergency Medicine. 49: 58–61. doi:10.1016/j.ajem.2021.05.054. PMC 8143907. PMID 34062319.
  8. ^ "AstraZeneca COVID-19 Vaccine (AZD1222)" (PDF). ACIP COVID-19 Emergency Meeting. AstraZeneca. 27 January 2021. Archived (PDF) from the original on 27 January 2021. Retrieved 16 April 2021.
  9. ^ "Vaxzevria (previously COVID-19 Vaccine AstraZeneca) EPAR". European Medicines Agency (EMA). 25 January 2021. Archived from the original on 21 April 2021. Retrieved 16 April 2021. The name of the vaccine was changed to Vaxzevria on 25 March 2021. Vaxzevria (COVID‑19 Vaccine (ChAdOx1-S recombinant) EMA/182334/2021 Archived 15 April 2021 at the Wayback Machine Text was copied from this source which is copyright European Medicines Agency. Reproduction is authorized provided the source is acknowledged.
  10. ^ "ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant) - Covishield". Serum Institute Of India. Archived from the original on 19 April 2021. Retrieved 16 April 2021.
  11. ^ "AstraZeneca ChAdOx1-S/nCoV-19 [recombinant], COVID-19 vaccine". World Health Organization (WHO). Archived from the original on 28 November 2021. Retrieved 28 November 2021.
  12. ^ a b Cite error: The named reference ema28mar was invoked but never defined (see the help page).
  13. ^ Marks P. "Joint CDC and FDA Statement on Johnson & Johnson COVID-19 Vaccine". Archived from the original on 20 May 2021. Retrieved 13 April 2021.
  14. ^ "Coronavirus (COVID-19) Update: FDA Limits Use of Janssen COVID-19 Vaccine to Certain Individuals". U.S. Food and Drug Administration. 5 May 2022. Archived from the original on 7 May 2022. Retrieved 7 May 2022.
  15. ^ Medical Director of AstraZeneca AB (13 April 2021). "Direct healthcare professional communication (DHPC): Vaxzevria (previously COVID-19 Vaccine AstraZeneca): link between the vaccine and the occurrence of thrombosis in combination with thrombocytopenia" (PDF). European Medicines Agency (EMA). Archived (PDF) from the original on 18 July 2022. Retrieved 13 April 2021.
  16. ^ "Research and analysis — Coronavirus vaccine - weekly summary of Yellow Card reporting". Medicines and Healthcare products Regulatory Agency (MHRA). 1 April 2021. Archived from the original on 20 May 2021. Retrieved 3 April 2020.
  17. ^ EMA (7 April 2021). EMA press conference 7th April — Conclusion of the assessment of the Pharmacovigilance Risk Assessment Committee (PRAC) of COVID-19 Vaccine AstraZeneca and thromboembolic events. European Medicines Agency (EMA). Archived from the original on 7 April 2021. Retrieved 7 April 2021 – via Youtube.
  18. ^ Agencies (29 April 2024). "Report: AstraZeneca admitted in court doc that Covid vaccine can cause rare side effect [NSTTV] | New Straits Times". NST Online. Archived from the original on 30 April 2024. Retrieved 29 April 2024.
  19. ^ "In a first, AstraZeneca admits its Covid vaccine can cause rare blood clots". The Independent. 30 April 2024. Archived from the original on 30 April 2024. Retrieved 30 April 2024.


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