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expert reaction to study looking at clinical features of rare clotting events after COVID-19 vaccines, ‘Vaccine-Induced Immune Thrombocytopenia and Thrombosis’ (VITT)

A study published in the New England Journal of Medicine (NEJM) looks at the clinical features of Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT).

This Roundup accompanied an SMC Briefing.


Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“In a sense there’s nothing new for the general public here – it was already known that the prognosis for someone with VITT is pretty bad, and it was also already known that it’s not at all common.  Though this paper does say something about the incidence rate of VITT in vaccinated people (“Thus, the approximate incidence of VITT was at least 1:100,000 among patients 50 years of age or older and at least 1:50,000 among patients in the younger group (<50 years of age)”), that’s pretty much the same as is said in the weekly coronavirus vaccine adverse effect reports from MHRA at  So nothing has really changed on the balance of risks and benefits of vaccination.”



‘Clinical Features of Vaccine-Induced Immune Thrombocytopenia and Thrombosis’ by Sue Pavord et al. was published in the NEJM at 22:00 UK time on Wednesday 11 August 2021.

DOI: 10.1056/NEJMoa2109908



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic.  My quote above is in my capacity as an independent professional statistician.”



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