Blood Clot Risk Higher for Covid-19 than Vaccines

An Oxford University has claimed that the risk of blood clotting is eight to 10 times higher following Covid-19 infection compared to coronavirus vaccines. 

And that Covid-19 patients are 100 times more likely to develop blood clots in the brain, known as cerebral venous thrombosis (CVT). 

The study, which looked at more than 500,000 Covid-19 patients, found that CVT occurred in 39 in one million patients. Thirty percent of these CVT cases occurred in Covid-19 patients below the age of 30. 

In comparison, CVT reportedly occurred in about five in one million people after they received their first doses of the AstraZeneca-Oxford’s Covid-19 vaccine. 

CVT occurred in four in one million people after receiving a Covid-19 mRNA vaccine, either the Pfizer-BioNTech or Moderna shot, based on a sample of over 480,000 people who took an mRNA vaccine. 

Hence, the risk of CVT from Covid-19 is about eight times higher than with the AstraZeneca vaccine, and about 10 times greater than with mRNA vaccines. 

AstraZeneca-Oxford’s coronavirus vaccine uses a chimpanzee adenovirus vaccine vector, whereas mRNA vaccines use messenger RNA technology. 

“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 we 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”, said Paul Harrison, professor of psychiatry and head of the Translational Neurobiology Group at the University of Oxford, one of the study’s lead authors. 

Dr Maxime Taquet, another lead author who is also from the Translational Neurobiology Group, said “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”. 

The study should go some way to reassuring people that the risks from vaccination are significantly lower than those associated with catching Covid-19, which can trigger many other complications, besides blood clots, and is estimated to have killed more than three million people globally since the start of the pandemic. 

Nonetheless, we should be cautious about making direct comparisons since data is still being gathered.