Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

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.

Coronavirus or virus causing blood clots to form in the blood system

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. They 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 seen 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 European Medicines Agency 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 – is 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.

To see the full data

NIHR OXFORD HEALTH BIOMEDICAL RESEARCH CENTRE NEWS

Please follow the link below to read the news on the NIHR BRC website.

Similar stories

Researchers Address Mental Health Effects of the Pandemic on Young People

In a new policy briefing, a team of researchers at King’s College London and Oxford University highlight the multiple effects that the COVID-19 pandemic has had on children and young people in the UK through their education and daily life, including challenges around social isolation, academic pressures, adjusting to online learning and coping with reopening of schools.

Simple Intervention Effectively Treats Depression During COVID 19

New research shows that even a very simple intervention, administered by non-specialists with just 15 hours of training, can effectively treat depression during COVID-19.

Over a Third of COVID-19 Patients Diagnosed with at Least One Long-COVID Symptom

A new study from the University of Oxford and the National Institute for Health Research (NIHR) Oxford Health Biomedical Research Centre (BRC) investigated long-COVID in over 270,000 people recovering from COVID-19 infection, using data from the US-based TriNetX electronic health record network.

Willingness of Children and Adolescents to have COVID-19 Vaccination

The OxWell School Survey 2021 highlights that younger children and adolescents are the least willing to have the COVID-19 vaccination. These young people come from the most socioeconomically deprived backgrounds, feel less belonging to their school community and think they have probably had COVID-19 already.

Mitigating Impacts of COVID-19 Pandemic on Parents and Carers During School Closures

The International Public Policy Observatory's (IPPO) Rapid Evidence Review has now been released. Co-authored by Professor Cathy Creswell, the Review was commissioned by the UK Department for Education following a recommendation from the Scientific Advisory Group for Emergencies (SAGE).