The EMA also initiated an assessment for all COVID‑19 vaccines used in the EU for immune thrombocytopenia (ITP), described as low blood platelet levels that could lead to bruising and bleeding, as a possible side effect, whilst also stating that up to this point no link with any COVID‑19 had been established.On 7 April 2021, the EMA determined that unusual blood clots with low blood platelets should be listed as very rare side effects of AZD1222, with WHO and UK EHRA issuing generally similar statements on the same day. None of the agencies found a confirmed causal link between the vaccine and these incidents at the time, but were listing them out of an abundance of caution.A highlight of minutes of the EMAs Pharmacovigilance Risk Assessment Committee (PRAC) concluding 9 April 2021, indicating they also were investigating four cases of unusual blood clots with low blood platelets, including one death, amongst people who had taken the Janssen COVID‑19 vaccine. The Janssen vaccine is approved but not yet deployed in the EU, though vaccinations are in progress in the US. PRAC has determined that it is not clear if there is a causal association. Should regulatory action prove necessary, PRAC have indicated the likely outcome would be an update to product information characteristics.
It is understood a special consent process will be developed by the Australian Government for people under 50 who choose to receive the AZD1222 vaccine. Studies
A study convened by a group of British hematologists on 19 March 2021, just two days after the acknowledgement of the condition, published its finding in The New England Journal of Medicine, establishing case definition criteria. The study included 294 participants who presented with symptoms of thrombocytopenia and thrombosis after receipt of the first dose of the Oxford–AstraZeneca COVID‑19 vaccine, showing an independent association between baseline platelet count and the presence of intracranial hemorrhage. The study established that 85% of the participants effected by the condition were aged younger than 60 years, and that those participants with a history of thrombosis or prothrombotic disorders did not appear to be at increased risk. The study showed an overall mortality rate of 22% and set out plans for additional research to determine the genetic factors that may increase risk of the condition and identify potential therapeutic agents. References
Notes
Footnotes
Further reading
Aleem A, Nadeem AJ (July 2021). "Coronavirus (COVID-19) Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)". StatPearls. PMID 34033367. Arepally GM, Ortel TL (July 2021). "Vaccine-induced immune thrombotic thrombocytopenia: what we know and do not know". Blood. 138 (4): 293–8. doi:10.1182/blood.2021012152. PMC 8172307. PMID 34323940. Iba T, Levy JH, Warkentin TE (January 2022). "Recognizing Vaccine-Induced Immune Thrombotic Thrombocytopenia". Crit Care Med. 50 (1): e80–e86. doi:10.1097/CCM.0000000000005211. PMC 8670081. PMID 34259661. Schultz NH, Sørvoll IH, Michelsen AE, Munthe LA, Lund-Johansen F, Ahlen MT,  et al. (June 2021).