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Blood Clot Link: Covid-19 ‘up to TEN times more likely to cause blood clot than having the jab’

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Catching the virus also raises the risk a hundred-fold compared to normal times, say scientists.

A study of more than 500,000 Covid patients found the chance of cerebral venous thrombosis (CVT) was 39 in a million.

In more than 480,000 people after receiving the Pfizer or Moderna mRNA vaccine, it fell to four in a million.

The potentially deadly complication was identified in around five in a million Britons getting the first dose of the Oxford-AstraZeneca.

It shows CVT is more common after Covid than in any of the comparison groups – with three in ten cases occurring in the under 30s.

The risk is ten and eight times greater compared to the mRNA and AZ-Oxford vaccines, respectively, and around 100 times higher than before the pandemic.

The virus was also linked to a clot that affects the liver, called portal vein thrombosis.

Lead author Professor Paul Harrison, a psychiatrist at Oxford University, said: “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?.’

“We have reached two important conclusions. Firstly, Covid-19 markedly increases the risk of CVT, adding to the list of blood clotting problems this infection causes.

“Secondly, the Covid-19 risk is higher than seeing with the current vaccines, even for those under 30; something that should be taken into account when considering the balances between risks and benefits for vaccination.”

The AstraZeneca data was based on the UK MHRA (Medicines and Healthcare products Regulatory Agency) monitoring system.

Other information analyzed used electronic health records stored in a US patient network called TriNetX.

It is known Covid-19 can cause blood clots in some individuals. Normally, they help stop bleeding after an injury.

A vessel produces proteins that attract platelets and other chemicals that clump together and allow healing.

But those that form in the absence of a wound can be fatal. They restrict the flow of blood to vital organs – which can lead to a stroke or heart attack.

Cases linked to Covid-19 have most often been seen in those who have been hospitalized with the disease.

It is believed the virus may activate platelets and endothelial cells that line the blood vessels. They are vital for starting the clotting process.

Coauthor Dr. Maxime Taquet, also from Oxford, said: “It is important to note this data should be interpreted cautiously.

“However, the signals that Covid-19 is linked to CVT, as well as portal vein thrombosis – a clotting disorder of the liver – is clear, and one we should take note of.”

An important factor that requires further research is whether the virus and vaccines lead to CVT by the same or different mechanisms.

There may also be under reporting or “miscoding” of CVT in medical records – adding to uncertainty, said the researchers.

Denmark has ceased giving the AstraZeneca vaccine amid concerns about rare blood clots – the first European country to do so fully.

The move is expected to delay the country’s vaccination program by several weeks.

Drug watchdog the European Medicines Agency last week announced a possible link with clots but said the risk of dying of Covid-19 was much greater.

Several European countries had previously briefly suspended the jab.

Most have now resumed vaccinations with AstraZeneca, but often with limits to older age groups.

On Tuesday, the US, Canada and the European Union paused the Johnson & Johnson vaccine for similar reasons over clotting.

South Africa has also paused its use, despite the Johnson & Johnson being its preferred vaccine because of its effectiveness against the South African variant.

For both AstraZeneca and Johnson & Johnson, the blood clot side effects are extremely rare.

The EU’s vaccine roll-out has been criticized by the World Health Organization (WHO) for being too slow, and there are concerns this latest delay could throw it into further turmoil.

So far 27 million people in the EU have been fully vaccinated.

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