15 April 2021
Cerebral venous thrombosis (CVT)is much more common after COVID-19
- COVID-19 leads to several times higher risk of CVT than current COVID-19 vaccines
- A similar pattern was seen for another serious clotting disorder, portal vein thrombosis.
Researchers at the University of Oxford have today reported that the risk of the rare blood clotting known as cerebral venous thrombosis (CVT) following COVID-19 infection is around 100 times greater than normal, several times higher than it is post-vaccination or following influenza.
The study authors, led by Professor Paul Harrison and Dr Maxime Taquet from Oxford University’s Department of Psychiatry and the NIHR Oxford Health Biomedical Research Centre, counted the number of CVT cases diagnosed in the two weeks following diagnosis of COVID-19, or after the first dose of a vaccine. The then compared these to calculated incidences of CVT following influenza, and the background level in the general population.
They report that CVT is more common after COVID-19 than in any of the comparison groups, with 30% of these cases occurring in the under 30s. Compared to the current COVID-19 vaccines, this risk is between 8-10 times higher, and compared to the baseline, approximately 100 times higher.
The breakdown comparison for reported cases of CVT in COVID-19 patients in comparison to CVT cases in those who received a COVID-19 vaccine is:
- In this study of over 500,000 COVID-19 patients, CVT occurred in 39 in a million patients.
- In over 480,000 people receiving a COVID-19 mRNA vaccine (Pfizer or Moderna), CVT occurred in 4 in a million.
- CVT has been reported to occur in about 5 in a million people after first dose of the AZ-Oxford COVID-19 vaccine.
- Compared to the mRNA vaccines, the risk of a CVT from COVID-19 is about 10 times greater.
- Compared to the AZ-Oxford vaccine, the risk of a CVT from COVID-19 is about 8 times greater.
However, all comparisons must be interpreted cautiously since data are still accruing.
Paul Harrison, Professor of Psychiatry and Head of the Translational Neurobiology Group at the University of Oxford, said: ‘There are concerns about possible associations between vaccines, and CVT, causing governments and regulators to restrict the use of certain vaccines. Yet, one key question remained unknown: ‘What is the risk of CVT following a diagnosis of COVID-19?’.
‘We’ve reached two important conclusions. Firstly, COVID-19 markedly increases the risk of CVT, adding to the list of blood clotting problems this infection causes. Secondly, the COVID-19 risk is higher than see with the current vaccines, even for those under 30; something that should be taken into account when considering the balances between risks and benefits for vaccination.’
Dr Maxime Taquet, also from the Translational Neurobiology Group, said: ‘It’s important to note that this data should be interpreted cautiously, especially since the data on the Oxford-AstraZeneca vaccine come from UK MHRA monitoring, whereas the other data uses the TriNetX electronic health records network. However, the signals that COVID-19 is linked to CVT, as well as portal vein thrombosis – a clotting disorder of the liver – are clear, and one we should take note of.’
An important factor that requires further research is whether COVID-19 and vaccines lead to CVT by the same or different mechanisms. There may also be under-reporting or mis-coding of CVT in medical records, and therefore uncertainty as to the precision of the results. Full data are available from https://osf.io/a9jdq/
Notes to Editors:
The full manuscript is available at: https://osf.io/a9jdq/
For further information, or to speak with the researchers, contact: Gen Juillet, Media Relations Manager, email@example.com
Work supported by NIHR Oxford Health Biomedical Research Centre.
About the University of Oxford
Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the fifth year running, and at the heart of this success is our ground-breaking research and innovation.
Oxford is world-famous for research excellence and home to some of the most talented people from across the globe. Our work helps the lives of millions, solving real-world problems through a huge network of partnerships and collaborations. The breadth and interdisciplinary nature of our research sparks imaginative and inventive insights and solutions.
Through its research commercialisation arm, Oxford University Innovation, Oxford is the highest university patent filer in the UK and is ranked first in the UK for university spinouts, having created more than 200 new companies since 1988. Over a third of these companies have been created in the past three years.
Oxford Health NHS Foundation Trust (OHFT) Oxford Health NHS Foundation Trust (OHFT) provides physical, mental health and social care for people of all ages across Oxfordshire, Buckinghamshire, Swindon, Wiltshire, Bath and North East Somerset. Our services are delivered at community bases, hospitals, clinics and people’s homes. We focus on delivering care as close to home as possible. As a leading teaching, training and research trust, we have close links to Oxford and Oxford Brookes, Buckinghamshire, Reading and Bath universities. We are part of the Oxford Academic Health Science Centre, working closely with our university colleagues to translate their findings into clinical care as quickly as possible, enabling people using our services to benefit from the latest advances in healthcare.
We host the NIHR Oxford Health Biomedical Research Centre with Oxford University, and aim to bring the best science to the complex problems of mental disorders and dementia. We also host the Collaboration for Leadership in Applied Health Research and Care (CLAHRC) Oxford; a partnership between universities, healthcare commissioners and providers, charities and industry targeting health and social care problems in Oxfordshire and the Thames Valley. www.oxfordhealth.nhs.uk
The National Institute for Health Research (NIHR) is the nation's largest funder of health and care research. The NIHR:
- Funds, supports and delivers high quality research that benefits the NHS, public health and social care
- Engages and involves patients, carers and the public in order to improve the reach, quality and impact of research
- Attracts, trains and supports the best researchers to tackle the complex health and care challenges of the future
- Invests in world-class infrastructure and a skilled delivery workforce to translate discoveries into improved treatments and services
- Partners with other public funders, charities and industry to maximise the value of research to patients and the economy
The NIHR was established in 2006 to improve the health and wealth of the nation through research, and is funded by the Department of Health and Social Care. In addition to its national role, the NIHR supports applied health research for the direct and primary benefit of people in low- and middle-income countries, using UK aid from the UK government.
This work uses data provided by patients and collected by the NHS as part of their care and support and would not have been possible without access to this data. The NIHR recognises and values the role of patient data, securely accessed and stored, both in underpinning and leading to improvements in research and care www.nihr.ac.uk/patientdata