There is a much higher risk of cerebral blood clots from COVID-19 infection than from vaccines against the disease, British researchers said on Thursday, after an interruption of inoculation due to reports of rare clots.
AstraZeneca (AZN.L) and Johnson & Johnson (JNJ.N) have seen very rare reports of cerebral venous sinus thrombosis (CVST) related to their vaccines. On Wednesday, the United States stopped vaccinations with the J&J shot while investigating a clot link, and Denmark dropped the AstraZeneca shot on the subject.
British and European regulators have stressed that the benefits of vaccination outweigh the risks.
A study of 500,000 patients with COVID-19 found that CVST had occurred at a rate of 39 people over a million after infection, the researchers said. This compares with European Medicines Agency (EMA) figures showing that 5 out of every million people reported CVST after receiving AstraZeneca’s shot.
The researchers said in a pre-printed study that the risk of CVST was 8-10 times higher after COVID-19 infection than that of existing vaccines against the disease.
“The risk of having one (CVST) after COVID-19 appears to be substantially and significantly higher than that which occurs after receiving the Oxford-AstraZeneca vaccine,” Maxime Taquet of the Oxford Department of Psychiatry told reporters.
The study was based on a U.S. health database and therefore did not accumulate new data on the risk of clots from the AstraZeneca vaccine directly, as the shot is not developing there.
Taquet said the CVST mortality rate was around 20% whether it occurred after COVID-19 infection or was vaccinated, indicating that clots were the main risk factor.
Regulators had also observed low platelet levels in vaccine side effects reports, but researchers said data were limited on whether this was also the case in those who reported CVST after infection.
The researchers noted that COVID-19 was associated with more common clotting disorders than CVST, such as stroke, and that the recent debate over vaccines had lost sight of the severity of the disease.
“The importance of this discovery is that it brings it back to the fact that it is a really horrible disease, as there are a wide variety of effects, including an increased risk (CVST),” said John Geddes, director of the NIHR Oxford Health Biomedical Research Center
The research team, from Oxford University, said it was working independently of the Oxford vaccination team that developed the AstraZeneca shot.
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