Risk of the rare blood clots reported during COVID-19 vaccine rollouts is higher when contracting the virus, researchers at the University of Oxford have shown.
The study, led by departments not linked to the AstraZeneca PLC (LON:AZN) jab, counted the number of cerebral venous thrombosis (CVT) cases diagnosed in the two weeks following diagnosis of COVID-19, or after the first dose of a vaccine.
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They were then compared to calculated incidences of CVT following influenza, and the background level in the general population.
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 university stressed that all comparisons must be interpreted cautiously since data are still accruing.
“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?” said Paul Harrison, Professor of Psychiatry and Head of the Translational Neurobiology Group.
Shares in AstraZeneca rose 1% to 7,378.66p on Thursday afternoon.