Higher risk of brain clots from Covid-19 than from vaccine: UK researchers

LONDON • There is a much higher risk of brain blood clots from Covid-19 infection than there is from vaccines against the disease, British researchers said, after the roll-out of inoculation was disrupted by reports of rare clots.

AstraZeneca and Johnson & Johnson have both seen very rare reports of cerebral venous sinus thrombosis (CVST) linked to their vaccines.

A study of 500,000 Covid-19 patients found that CVST had occurred at a rate of 39 people out of a million following infection, researchers said. That compares with European Medicines Agency figures showing that five in a million people reported CVST after receiving AstraZeneca's shot.

The researchers said in a pre-print study that the risk of CVST was eight to 10 times higher after Covid-19 infection than it was from existing vaccines for the disease.

"The risk of having a (CVST) after Covid-19 appears to be substantially and significantly higher than it is after receiving the Oxford-AstraZeneca vaccine," Dr Maxime Taquet of the University of Oxford's department of psychiatry told reporters.

The study was based on a United States health database, and so did not accrue new data on the risk of clots from AstraZeneca's vaccine directly, as the shot is not being rolled out in the US.

Dr Taquet said that the mortality rate from CVST was about 20 per cent, whether it occurred after Covid-19 infection or a vaccine, indicating that the clots were the main risk factor.

Regulators had also observed low platelet levels in reports of vaccine side effects, but the researchers said data was limited on whether that was also the case in those reporting CVST after infection.

The researchers highlighted that Covid-19 was associated with more common clotting disorders than CVST, such as strokes, and that recent debate around vaccines had lost sight of how bad the disease itself could be.

"The importance of this finding is it brings it back to the fact this is a really horrible illness as a whole variety of effects, including increased risk of (CVST)," said Professor John Geddes, director of the NIHR Oxford Health Biomedical Research Centre.

REUTERS