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New evidence has emerged today linking COVID-19 vaccines to extremely rare cases of people who develop blood clots and low platelets within a few weeks of vaccination.
A team of researchers from the UK conducted an in-depth investigation of 22 patients who developed severe blood clots combined with a drop in blood platelets after receiving a dose of the AstraZeneca vaccine, now called Vaxzevria. They also tested an additional patient who showed clinical signs of platelet drop after vaccination. Almost all patients (22 of 23) tested unusual for antibodies against platelet factor 4, a signaling protein that helps the body coordinate blood clotting.
The presence of antibodies suggests that vaccines somehow trigger an autoimmune attack that causes the formation of large clots that decrease the supply of platelets to the blood.
The study and an editorial on the cases are published in New England Journal of Medicine.
This is at least the third study detailing the presence of these antibodies in patients with blood clots and low platelets after vaccination, and doctors say emerging evidence suggests that doctors should be alert to this new syndrome in anyone who has symptoms of blood clots anywhere in the country. the body, not just the brain.
James Zehnder, MD, director of the coagulation lab at Stanford University School of Medicine in California, said growing evidence pointing to an “inappropriate immune response” was quite remarkable. He did not participate in the investigation.
Zehnder says why this syndrome, which appears to be a type of autoimmune attack on a blood-signaling protein, develops in a small number of people after getting the anticoagulant heparin or a vaccine against COVID-19 is still a mystery.
He says that while catastrophic cases of large clots in areas of the brain where doctors don’t usually see them stand out, he wonders if other less obvious cases won’t be detected.
“So the question is, you know, how much of this happens in a more subtle way? And so I don’t think the true magnitude is known,” he says, noting that it will be important in the coming weeks and months to find out. if certain groups of people are at higher risk than others, such as young women. “Now there are a lot more questions than answers,” he says.
Main symptoms to see
Symptoms to consider include shortness of breath, headaches, dizziness, muscle weakness or abdominal pain, back pain or nausea and vomiting in anyone within 3 weeks of vaccination, including men.
People who have not been vaccinated can also develop this type of clot, called cerebral venous sinus thrombosis. These cases, whether or not after a vaccine, are extremely rare. On average each year, there are two to 14 cases of these clots in vessels that drain blood from the brain for every million people, according to Peter Marks of the U.S. Food and Drug Administration.
Doctors say that, in general, all vaccines authorized to protect people against the new coronavirus are extremely safe. In fact, the risk of developing a life-threatening blood clot is much higher with COVID than with the vaccine.
“The odds of this happening to you are between 1 and 100,000 to 1 in a million,” said John Wherry, PhD, director of the Institute of Immunology at the University of Pennsylvania in Philadelphia. “If you’re American, the odds of dying from COVID are 1 in 600,” Wherry continued, citing statistics on COVID cases and deaths in the U.S. maintained by Johns Hopkins University.
In a presentation presented at the Centers for Disease Control and Prevention this week, representatives of vaccine maker Johnson & Johnson said they had found a 25-year-old man who developed a rare clot in his brain and lower platelets during his clinical trial. . When they returned and tested their stored blood, they found that it also had the developing platelet factor 4 antibodies, making it the 7th known case related to this vaccine in the United States. He has since recovered.
Investigators initially dismissed her case as unrelated to the vaccine because another study participant, a 24-year-old woman, also developed a brain clot similar to the brain, but she was part of the placebo group. He had recently been prescribed birth control pills, which increase the risk of blood clots and stroke like the one he suffered.
An eighth case, possibly linked to the Johnson & Johnson vaccine, is still being investigated in the United States.
Wherry said it is not uncommon for these rare cases not to be detected in clinical trials, which involved tens of thousands of people. He said that sometimes very rare events only come to light when a drug or device is used in millions, as vaccines have now been.
He said the fact that these facts were detected means that security surveillance systems are working.
“We’re doing everything right,” he said. “It’s unfortunate and traumatic if it happens, but in terms of the risk-benefit relationship, we still have to put the numbers into perspective and now, having captured many of these events, we now have an idea of what to do when we see them. , “Added Wherry.
Cases of the United Kingdom
Of the 22 cases identified in the new UK study, 16 (70%) were under 50 and 14 (61%) were women. They were all healthy before developing rare clots. None were taking drugs related to clotting or bleeding. Some came in with mild bruises and small red spots called petechiae, which indicate bleeding on the skin.
This constellation of symptoms, a severe coagulation combined with a platelet drop, is not new. Doctors recognize it as a sign that someone has a severe and rare reaction to anticoagulant heparin. In patients taking heparin, it is called HIT, due to heparin-induced thrombocytopenia.
Doctors investigating the symptoms as part of new COVID vaccines have called it vaccine-induced thrombotic thrombocytopenia or VITT.
The authors of the UK study found that a cure point test commonly used to detect HIT (the HemosIL AcuStar HIT IgG assay) was often negative for patients with VITT. They say VITT should be confirmed by another type of test, an ELISA or an enzyme-linked immunosorbent assay.
Patients with VITT also need a different type of treatment than would normally be given to a person experiencing dangerous blood clots or bleeding. Giving platelets, for example, to stop the bleeding could make the situation worse. Instead, they need IVIG treatment to mitigate the apparent autoimmune attack. Researchers say that until more information is known, it is also prudent to use anticoagulants other than heparin to treat clots.
Wherry says he is not surprised to see some men affected, but that, so far, the emerging image suggests that women are at greater risk.
She says women are usually more prone to autoimmune diseases and are also more susceptible to blood clots due to the hormone estrogen.
“So it fits with that idea that it can be, you know, an indicator of some autoimmune bias,” he said.
NEJM. Published online April 16, 2021. Full text, Editorial
Several co-authors report receiving personal fees from one or more of the following companies: Bayer, Bristol Myers Squibb, Daiichi Sankyo, Pfizer, Novartis, Octapharma, Sanofi, Sobi, Alexion, and Takeda. A co-author reports on grants from Shire and Novartis; a co-author reports on other financial relationships with GSK; and a co-author reports a patent test for bacterial meningitis based on a blood test, filed pending patent.
Wherry reports consulting agreements with and / or is a scientific advisor for Merck, Roche, Pieris, Elstar and Surface Oncology. He has a patent license agreement on the PD1 route with Roche / Genentech and is the founder of Arsenal Biosciences.
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