AstraZeneca’s vaccine may trigger rare immune response that leads to clots in some people
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 found the shot can in very rare cases cause the body to attack its own blood platelets, triggering deadly clots in the brain.
The experts said that patients who suffer headaches or dizziness four days after getting the jab could be quickly diagnosed with a blood test and treated with blood thinning medication.
The German team, which collaborated with scientists in the UK, Ireland and Austria, said its findings meant people should not fear the vaccine. However, Norway’s health ministry has used the results to extend its ban on the British-made vaccine.
More than a dozen European countries suspended the AZ jab last week after more than 30 patients suffered 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 anymore frequently than they would in the general population, a claim which has been echoed by medical regulators in the UK and EU.
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)
Regulatory reports show that blood clot diagnoses are about equally likely after either the two jabs being used in the UK – slightly higher for Pfizer – and scientists insist the risk is no higher than a random person in the population could expect, meaning the vaccine remains safe. Rates of death soon after vaccination appear higher for AstraZeneca’s vaccine but this is likely because it is used in care homes and the people receiving it are naturally more likely to die of any reason
Figures from AstraZeneca and the European Medicines Agency show the number of blood clot-related conditions from 17million doses dished out in the UK and Europe up to March 13
The research teams from Oslo and Greifswald University believe the vaccine causes the body to produce antibodies – normally used to fight off infections or pathogens – which attack them.
To compensate, the body then overproduces platelets which causes the blood to thicken and risks clotting. But the experts have admitted they ‘don’t know why this is happening’.
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.
Neither the German nor the Norwegian findings were published or peer reviewed.
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 after getting 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 CVT had splanchnic vein thrombosis, which occurs when a vein in the abdomen clots.
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.
None of this group has these 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’s reached the same conclusion, that is due to antibodies causing an overreaction to the vaccine.
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
‘Our theory that this is a strong immune response that most likely comes after the vaccine,’ Holme said, according to an NPR translation.
‘There is no other thing than the vaccine that can explain this immune response.’
It comes on the heels of news that Canada is suspending use of the vaccine 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, AstraZeneca today 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.
AstraZeneca has now sent the amended results to the US Data and Safety Monitoring Board, the secretive committee vetting Covid vaccines that raised the alarm about the original numbers. It feared AstraZeneca had left out some cases that may have skewed the results.
Scientists said the original statement, issued by the National Institute of Allergy and Infectious Diseases (NIAID) on behalf of the DSMB, was highly ‘unusual’ because any discussions about findings are usually held behind closed doors.
The small revision to the efficacy rate will go a long way to putting the vaccine back on track for US approval, with the firm hoping it will be given the green light in the coming weeks. Britain’s regulators gave it the sign off in December.
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