Called sinus vein thrombosis (CVST), it characterises what happens when a clot forms in the cerebral vein of the brain.
The MHRA has assured that this can occur naturally in people who have not been vaccinated.
It added that a “rigorous” scientific review had found no evidence that the AstraZeneca vaccine against COVID-19 caused blood clots in veins.
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The five men, aged between 19 and 59, suffered from Cerebral Venous Sinus Thrombosis (CVST), although the MHRA said it did not know whether it had been directly caused by the vaccine.
The regulator urged people to continue getting the vaccine, adding that the link is unproven and the benefits far outweigh the risks of not getting vaccinated.
Fewer than one in a million cases had been recorded after a jab and a causal link had not been established, it noted.
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He said: “We have had five reports of a unique form of blood clot, Cerebral Venous Sinus Thrombosis, concurrent with low blood platelets. This is similar to some of the cases reported through Europe.
“What we don’t know is whether these have been caused by the vaccines. We are working closely to determine this, because these illnesses do very rarely happen naturally. We do know that after more than five million this is extremely rare – less than one in a million cases of this even after vaccination.
“Covid disease is associated with significant mortality. Both vaccines are highly effective. And there is no proven causal association with what is still an extremely rare medical event.”
When will I receive the vaccine?
The NHS is currently offering the COVID-19 vaccine to people most at risk from coronavirus.
In England, the vaccine is being offered in some hospitals and pharmacies, at local centres run by GPs and at larger vaccination centres. More centres are opening all the time.
It’s being given to:
- People aged 50 and over
- People at high risk from coronavirus (clinically extremely vulnerable)
- People who live or work in care homes
- Health and social care workers
- People with a condition that puts them at higher risk (clinically vulnerable)
- People with a learning disability
- People who are a main carer for someone at high risk from coronavirus.
The order in which people will be offered the vaccine is based on advice from the Joint Committee on Vaccination and Immunisation (JCVI).