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New evidence has emerged today linking COVID-19 vaccines to extremely rare cases of people who develop low blood clots and platelets within weeks of vaccination.
A team of researchers in 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 AstraZeneca vaccine, now called Vaxzevria. They also tested an additional patient who showed clinical signs of a decrease in blood platelets after vaccination. Almost all patients – 22 out of 23 – tested positive for unusual antibodies to 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 then decrease the platelet intake in the blood.
The study and an editorial on 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 low blood clots and platelets after vaccination, and doctors say emerging evidence suggests that doctors should remain vigilant for this new syndrome in anyone with symptoms of blood clots. blood anywhere in the body, not just the brain.
James Zehnder, MD, director of the coagulation laboratory at Stanford University School of Medicine in California, said growing evidence of an “maladaptive immune response” was quite remarkable. He was not involved in the research.
Zehnder says why this syndrome, which appears to be a kind of autoimmune attack on a blood signaling protein, develops in a small number of people after receiving anticoagulant heparin or a COVID-19 vaccine. mystery.
He says that while catastrophic cases of large clots in areas of the brain where doctors do not usually see them stand out, he wonders if other less obvious cases will go undetected.
“Then the question is, you know, how much of this happens in a more subtle way? And so I don’t think the true extent of it 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. “There are many more questions than answers now,” he says.
Key symptoms to watch out for
Symptoms to follow include difficulty breathing, headache, dizziness, muscle weakness or abdominal pain, back pain or nausea and vomiting in anyone within 3 weeks of vaccinations, including men.
People who have not been vaccinated can also develop these types of clots, called cerebral venous sinus thrombosis. These cases – whether or not they occur after a vaccine – are extremely rare. On average, each year, there are two to 14 cases of these blood clots in the vessels that drain blood from the brain for every million people, according to Peter Marks of the US Food and Drug Administration.
Doctors say that, overall, all vaccines authorized to protect people from the new coronavirus are extremely safe. In fact, the risk of developing a life-threatening blood clot is much higher with COVID than with a vaccine.
“The chances of this happening to you are between 1 and 100,000 to 1 in 1 million,” said John Wherry, Ph.D., director of the Institute of Immunology at the University of Pennsylvania in Philadelphia. “If you are American, the chances of dying from COVID are 1 in 600,” Wherry continued, citing statistics on COVID cases in the United States and deaths maintained by Johns Hopkins University.
In a presentation to the Centers for Disease Control and Prevention this week, representatives of vaccine maker Johnson & Johnson said they found a 25-year-old man who developed a rare brain clot and low platelets during the clinical trial. When they returned and tested the stored blood, they found that it also had antibodies that revealed platelet factor 4, making it the 7th known case of that vaccine in the United States. He has recovered since then.
Investigators initially dismissed her case as unrelated to the vaccine because another study participant, a 24-year-old woman, also developed a similar blood clot in her brain, but she was in the placebo group. . He was recently prescribed birth control pills, which increase the risk of blood clots and strokes such as those suffered.
An eighth case, possibly related to the Johnson & Johnson vaccine, is still being investigated in the United States.
Wherry said it was not surprising that these rare cases had not been detected in clinical trials, which involved tens of thousands of people. He said that very rare events sometimes come to light only when a drug or device is used in millions, as vaccines have now been.
He said that the fact that these events were detected at all means that the 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 ratio, we still have to put the numbers into perspective and now that we’ve caught many of these events, we now have an idea of what to do when we see them, “Added Wherry.
Cases in the UK
Of the 22 cases identified in the new study in the UK, 16 (70%) were under the age of 50 and 14 (61%) were women. They were all healthy before the appearance of rare clots. None took medication for coagulation or bleeding. Some came with light bruises and small red spots called petechiae, which indicate bleeding under the skin.
This constellation of symptoms, severe coagulation combined with a decrease in platelets, 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, for heparin-induced thrombocytopenia.
Doctors investigating the symptoms of the new COVID vaccines have called it vaccine-induced thrombotic thrombocytopenia or VITT.
The study’s authors in the UK found that a point-of-care test commonly used to detect HIT – the HemosIL AcuStar HIT IgG test – was often negative for patients with VITT. They say that VITT must 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 a person with dangerous blood clots or bleeding. Offering platelets, for example, to stop the bleeding could make the situation worse. Instead, they need IVIG treatment to alleviate the apparent autoimmune attack. Researchers say that until more is known, it is prudent to use anticoagulants other than heparin to treat clots.
Wherry says he is not surprised to see a few men affected, but that, so far, the emerging image suggests that women are at greater risk.
He says women tend to be more prone to autoimmune diseases and are also more susceptible to blood clots due to the hormone estrogen.
“So it fits with the idea that it can be, you know, an indicator of an autoimmune tendency,” he said.
NEJM. Published online April 16, 2021. Full text, Editorial
Several co-authors state that they receive personal taxes from one or more of the following companies: Bayer, Bristol Myers Squibb, Daiichi Sankyo, Pfizer, Novartis, Octapharma, Sanofi, Sobi, Alexion and Takeda. One co-author reports Shire and Novartis grants; a co-author reports other financial relations with GSK; and a co-author reports a patent test for bacterial meningitis based on a blood test filed for the current 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 path with Roche / Genentech and is the founder of Arsenal Biosciences.
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