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Immune response may explain rare clots after AstraZeneca vaccine

Daily Mail logo Daily Mail 29/03/2021 Mary Kekatos Senior Health Reporter For Dailymail.com and Connor Boyd Assistant Health Editor For Mailonline
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European scientists believe they have an explanation for the blood clots reported in a tiny number of people who received Oxford-AstraZeneca's coronavirus vaccine. 

Two separate research teams in Germany and Norway claimed the shot may, in very rare cases, cause the body to attack its own blood platelets, triggering deadly clots in the brain. 

Patients who endured the brain clot were likely to suffer severe headaches, dizziness and loss of vision in the days after being vaccinated. 

Experts say the condition — which has not been proven to be caused by the jab and may be occurring naturally because millions of people are being vaccinated — can be diagnosed with a simple blood test and quickly treated with blood-thinners. 

German academics, who collaborated with scientists in the UK, Ireland and Austria, said its findings meant people should not fear the vaccine. Norway's health ministry, however, has used the results to temporarily extend its ban on the jab while further tests are done.

More than a dozen European countries suspended AZ's jab last week after more than 30 cases of cerebral sinus vein thrombosis (CSVT). Most of the patients were under the age of 55 and a disproportionate number were women. 

The extremely rare condition, which sees a major vein in the brain become blocked, is thought to have affected fewer than one in 2million vaccinated people. 

AstraZeneca still maintains that the clots are not occurring any more frequently than they would in the general population, a claim which has been echoed repeatedly by medical regulators in the UK and EU to hammer home the message the jab is safe. 

a hand holding a bottle: German researchers found signs of a type of antibody that forms in response to inflammation in some people and attacks platelets in nine people who developed clots after getting the AstraZeneca shot. These antibodies destroy the platelets and, to make up for the loss, the body overproduces platelets, causing them to clot (file)

German researchers found signs of a type of antibody that forms in response to inflammation in some people and attacks platelets in nine people who developed clots after getting the AstraZeneca shot. These antibodies destroy the platelets and, to make up for the loss, the body overproduces platelets, causing them to clot (file)
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WHAT IS CSVT? 

Cerebral sinus vein thrombosis (CSVT) is an extremely rare type of blood clot in the brain.

It occurs when the vein that drains blood from the brain is blocked by a blood clot, resulting in potentially deadly bleeding on the brain.  

Symptoms can quickly deteriorate from a headache, blurred vision and faintness to complete loss of control over movement and seizures. 

John Hopkins University estimates it affects five in a million people in the US every year, which would suggest 330 patients in Britain suffer from the condition annually.

According to the university, it can affect patients with low blood pressure, cancer, vascular diseases and those prone to blood clotting. Head injuries can also trigger the condition. 

Britain's regulator said CSVT is so rare they aren't even sure how common it is in the general population.

The research teams from Oslo and Greifswald University believe the jab could cause the body to produce antibodies — normally used to fight off infections or pathogens — which mistake platelets in the blood for foreign invaders and attack them.

To compensate, the body then overproduces platelets, causing the blood to thicken — which risks clotting. 

The experts have admitted they 'don’t know why this is happening'.

But the researchers say the phenomenon is similar to one that can occur in heparin-induced thrombocytopenia (HIT), when sufferers take a drug called heparin.

Among those with HIT, the drug triggers the immune system to produce antibodies that activate platelets.


Video: Immune response 'plausible' explanation for AstraZeneca clots says EMA chief (AFP)

Drugs other than heparin can cause clotting disorders that strongly resemble HIT, and researchers suspect that in rare cases, the AstraZeneca vaccine may be another such trigger.

Neither the German nor the Norwegian findings were published or peer-reviewed — a crucial scientific practice that irons out key holes in studies.

Andreas Greinacher, professor of transfusion medicine at the Greifswald University Clinic, said his team would submit the results for publication to the British medical journal The Lancet in the coming days. 

The German team looked at nine cases of blood clots reported in Germany and Austria in patients who had been given the AstraZeneca vaccine.

Seven patients had cerebral venous thrombosis (CVT), which is a blood clot in the brain; one had a pulmonary embolism, and one had a clot on a vein in their abdomen. 

Blood samples from four of the individuals showed they had the same kind of antibodies that activate platelets and initiate clotting in HIT. 

These samples were then compared to 20 individuals who were given the AstraZeneca vaccine and did not experience blood clots. 

Cerebral sinus vein thrombosis occurs when the vein that drains blood from the brain (shown) is blocked by a blood clot, resulting in potentially deadly bleeding on the brain © Provided by Daily Mail Cerebral sinus vein thrombosis occurs when the vein that drains blood from the brain (shown) is blocked by a blood clot, resulting in potentially deadly bleeding on the brain

Canada pauses use of AstraZeneca's Covid vaccine for under-55s over lingering blood clot fears

Canada is pausing its use of AstraZeneca's Covid vaccine for people younger than 55, amid 'safety concerns.'

The country's National Advisory Committee on Immunization is recommended the pause, citing lingering worries over rare blood clots, and Health Canada officially called for the suspension on Monday.

So far, no cases of the rare but life-threatening clotting condition have been reported in Canada.

Canada is set to receive a shipment of 1.5million doses of AstraZeneca's vaccine from the US, which has not yet authorized the shot.

It comes after European health regulators ruled that concerns that the shot might cause blood clots were unfounded. Before that, some European countries thought paused use of the shot in elderly people, due to claims it was ineffective.

None of that group had the antibodies. 

The researchers advise anyone receiving the AstraZeneca vaccine to keep an eye out for any bruising, swelling or headaches that begin four or more days after being immunized. 

If vaccine recipients identify any of these symptoms early on, the situation can be treated easily by a doctor.

Meanwhile, a group of researchers in Norway say have been studying three cases of blood clots post-AstraZeneca vaccination. 

Professor Pål Andre Holme of Oslo University Hospital told Norwegian newspaper VG that he had reached the same conclusion, with an antibody overreaction to blame. 

'Our theory that this is a strong immune response that most likely comes after the vaccine,' Professor Holme said, according to an NPR translation. 

'There is no other thing than the vaccine that can explain this immune response.'

The findings come on the heels of news that Canada is suspending use of the jab for people under age of 55 due to blood clot fears.

Some countries, such as Germany, France and Italy, resumed vaccinations with AstraZeneca’s shot last week, with the added warning that it could in very rare circumstances cause clotting. 

Others, including Norway, Sweden and Denmark, have still not resumed their rollouts.

AstraZeneca's vaccine is still waiting on US regulatory approval. 

The process was delayed last week after the Anglo-Swedish pharmaceutical giant was accused by US watchdogs of cherry-picking data to make it seem more effective than it actually was in the American arm of its human trials.

On the back of the criticism, AZ revised the headline efficacy figure slightly, from 79 to 76 per cent at stopping symptomatic infections. 

The data was based on the final results of the exact same 32,000-person trial.

UK experts described the differences as 'tiny', adding that it was normal for results to fluctuate as more data from the studies came in. They also criticised US officials for potentially fuelling vaccine hesitancy. 

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