YOU’RE up to ten times more at risk of getting a blood clot from Covid-19 than the AstraZeneca vaccine, scientists say.
A study looked at the odds of getting a brain blood clot, called CVST, in people who had been diagnosed with Covid compared with those who had a vaccine.
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The risk of a brain blood clot, CVST, in different groups of people. It shows the risk and the range in brackets
You’re up to ten times more at risk of getting a blood clot from Covid-19 than the AstraZeneca vaccine, scientists sayCredit: AFP
It showed the risk of a brain blood clot after the AstraZeneca vaccine was five in a million, and four in a million after vaccines from Pfizer or Moderna.
For people who had Covid, the risk was almost 40 in a million.
Researchers at Oxford – the same university that created the vaccine – said either after the coronavirus or vaccine, the risk of a brain blood clot in the following two weeks was very rare.
But comparing the two, they said the risk was “substantially and significantly higher” after Covid – which is avoidable with a vaccine.
The team also looked at rates of clotting in people who had the flu, which was zero.
And they said the risks of CVST after Covid was “many-fold” higher than in the general population, perhaps up to 100 times higher.
A similar pattern was seen for another serious clotting disorder, portal vein thrombosis, which affects blood supply to the liver. The condition has not been flagged by regulators.
But the team cautioned their results, which haven’t yet been published in a medical journal, had some limitations.
Not all cases studied had CVST with the addition of low blood platelets, called thrombocytopenia.
It is this “unusual combination” of conditions that the AZ jab has been linked to, and not CVST alone.
It may explain why the risk was similar between the AstraZeneca jab, and those from Pfizer and Moderna.
The latter two jabs have not been linked to the concerning cases of CVST with low blood platelets.
The researchers said therefore that their findings “cannot contribute” to the debate around the AstraZeneca vaccine and its links to unusual blood clot events.
However, they suggested the key takeaway of their study was the risks of catching Covid outweighed the risks of getting a jab.
It echoes the reassurances from regulators in both Europe and the UK, that people should feel safe to get the jab because the benefits are so much greater than any potential, and extremely rare, risk.
Study author Paul Harrison, professor psychiatry at the University of Oxford, told journalists: “We can’t say from our data what the baseline risk is in the type of people you can imagine trying to make this decision.
“All the evidence we have is that the risks of covid are so much greater than whatever the risks of the vaccine might be.
“I think it would be a very logical decision for me to say, ‘well I accept those risks may be present, but they are clearly much less than the risk of catching Covid’.
“Unfortunately you might think you’re not going to catch it, but anybody is at risk of catching Covid in the current climate.”
What are the risks of a brain blood clot?
According to the Oxford study:
Covid: 39 in a million (using 500,000 Covid patients)
AstraZeneca/Oxford vaccine: 5 in a million (
Pfizer or Moderna mRNA vaccines: 4 in a million (using 480,000 recipients)
Compared to the mRNA vaccines, the risk of a CVST from Covid is about 10 times greater.
Compared to the AstraZeneca/Oxford vaccine, the risk of a CVT from Covid is about eight times greater.
The chances of getting CVST due to Covid has not been studied before, making this study one of a kind.
But it has previously been stressed to people in fear of getting the AZ vaccine, that blood clots caused by Covid are not uncommon.
Professor Sir Munir Pirmohamed, chairman of the Commission on Human Medicines, said recent research has shown that clots on the lungs occur in 7.8 per cent of people who have Covid.
Clots in the legs – known as deep vein thrombosis (DVT) – happen in 11.2 per cent of sufferers.
And up to 30 per cent of people will get thrombocytopenia.
Almost a quarter (23 per cent) of patients who end up in intensive care with Covid “will have some form of clot”.
The Oxford study did not look at the Janssen vaccine, which is being investigated for a link to cases of CVST with low blood platelets.
The jab uses the same technology as the AstraZeneca vaccine, but is not yet in use in Europe or the UK.
After a “plausible link” was made between the AZ jab and unusual CVST cases, many countries have halted use of the jab in younger groups.
In the UK, people under 30 will be given an mRNA vaccine from either Pfizer or Moderna.
Although officials could not be certain, there are some signs young women are more at risk of the serious side effect.
The Oxford study said 30 per cent of the CVST cases after Covid were in people under 30 years old.
The team added the participants in either study groups – those who had Covid or a vaccine – were not age matched.
But researchers said they did not think this would skew the results, based on early analysis.