Researchers at Oxford University said Thursday that the risk of developing rare blood clots is higher after becoming infected with COVID-19 than it is for people who have been vaccinated.
The findings come in a new study published by the university, which helped develop the AstraZeneca vaccine that has now come under scrutiny for potential links to a brain blood clot known as cerebral venous sinus thrombosis (CVST).
After comparing the number of CVST cases in the two weeks following a COVID-19 diagnosis and after the first dose of a vaccine, Oxford reports that the risk of developing the blood clots is as much as 10 times greater following a COVID-19 infection than it is after a vaccination.
The researchers noted that compared to the Pfizer and Moderna vaccines, the risk of developing CVST is about 10 times greater, while the risk is about eight times higher when compared to the Oxford-AstraZeneca inoculation.
While the study noted that data on potential links between the vaccines and blood clots are still under review, Paul Harrison, head of Oxford’s Translational Neurobiology Group, said that Thursday’s findings “should be taken into account when considering the balances between risks and benefits for vaccination.”
The study comes after a wave of countries has limited the use of AstraZeneca’s vaccine to older age groups due to reports of blood clots.
On Wednesday, Denmark became the first European country to completely halt the use of the AstraZeneca shot after an investigation “showed real and serious side effects,” according to the Danish Health Authority.
A safety committee of the European Medicines Agency (EMA) said last week that a “possible link” exists between the AstraZeneca vaccine and blood clots, though it added that the benefits of the inoculation to protect against COVID-19 outweigh the risks.
Oxford’s study did not include data on the shot from Johnson & Johnson, which has been paused in the U.S. upon recommendations from health authorities that are reviewing six cases of blood clots among the 7 million people who received the shot.
An independent advisory group to the Centers for Disease Control and Prevention on Wednesday postponed making a recommendation on the Johnson & Johnson shot until there was more evidence on blood clots, likely prolonging the distribution of one of the three coronavirus vaccines federally approved for emergency use in the U.S.