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New evidence emerged today linking a vaccine for COVID-19 to the very rare cases of people with low blood clots. platelets within a few weeks of being vaccinated.

A team of researchers in the UK carried out an in-depth investigation of 22 patients who had serious blood clots combined with decreased blood platelets after receiving a dose of the AstraZeneca vaccine, now called Vaxzevria. They also tested additional patients who had clinical signs of decreased blood platelets after vaccination. Nearly all of the patients – 22 of 23 – tested positive for the unusual antibody to platelet factor 4, a signaling protein that helps the body coordinate blood clotting.

The presence of antibodies indicates that the vaccine somehow triggers an autoimmune attack that causes large clots to form which then reduces the supply of platelets in the blood.

Study and editorial about the cases published on New England Journal of Medicine.

This is at least third study detailed the presence of these antibodies in patients with blood clots and low platelets after vaccination, and doctors say emerging evidence suggests that doctors should remain alert for this new syndrome in anyone with symptoms of blood clots anywhere in the body, not just in the brain. .

James Zehnder, MD, director of the coagulation laboratory at Stanford University School of Medicine in California, says there is growing evidence that the “maladaptive immune response” is quite extraordinary. He was not involved in the research.

Zehnder says why this syndrome, which appears to be a kind of autoimmune attack on blood signaling proteins, develops in a small number of people after they get an anticoagulant. heparin or a vaccine for COVID-19 is still a mystery.

He said that while catastrophic cases of large lumps in areas of the brain where doctors usually don’t see them stand out, he wonders if other, less obvious cases have gone undetected.

“Then the question is, you know, how much of this is going on in a more subtle way? So I think the real magnitude is unknown,” he said, noting that this will be important in the coming weeks. and months to find out if certain groups of people are at a higher risk than others, such as young women. “There are more questions than answers now,” he said.

Main Symptoms to Pay Attention to

Symptoms to watch for include shortness of breath, headache, dizziness, muscle weakness, or stomach pain. back pain, or nausea and vomiting in anyone within 3 weeks of vaccination, including men.

People who haven’t been vaccinated can also develop a type of clot called a cerebral venous sinus thrombosis. These cases – whether they occur after vaccination or not – are very rare. On average each year, there are two to 14 cases of these 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 passed to protect people from the new coronavirus are very safe. In fact, the risk of developing life-threatening blood clots is much higher with COVID than with vaccines.

“The odds of this happening to you are between 1 and 100,000 to 1 in 1 million,” says John Wherry, PhD, director of the Institute for Immunology at the University of Pennsylvania in Philadelphia. “If you are an American, the chance of dying from COVID is 1 in 600,” continued Wherry, citing statistics on US COVID cases and deaths administered by Johns Hopkins University.

In a presentation to the Centers for Disease Control and Prevention this week, representatives from the vaccine manufacturer Johnson & Johnson said they had found a 25-year-old man who developed rare clots in his brain and low platelets during their clinical trials. When they came back and tested the stored blood, they found he also had signaling antibodies to platelet factor 4, making him the 7th case known to be linked to the vaccine in the United States. He has recovered.

Investigators initially dismissed her case as unrelated to vaccines 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’s just been prescribed it birth control pills, which increase a woman’s risk of blood clots and strokes like she has.

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 went undetected in clinical trials involving tens of thousands of people. He said that very rare events are sometimes only revealed when drugs or devices are used in the millions, such as vaccines now.

He said that the fact that this event was detected completely means that the safety surveillance system is working.

“We did everything right,” he said. “It would be unfortunate and traumatic if that happened, but in terms of the risk to benefit ratio we still have to put the numbers in perspective and now that we have captured many of these events we now have an idea of ​​what to do when we see it,” Wherry added. .

British case

Among the 22 cases identified in the new UK study, 16 (70%) were under 50 years of age, and 14 (61%) were women. All were healthy before developing rare clots. No one was taking drugs that were linked to clotting or bleeding. Some present with light bruising and small red spots called petechiae, which indicate bleeding under the skin.

This collection of symptoms, severe clotting combined with decreased platelets, is nothing new. Doctors recognize it as a sign that a person is experiencing a rare, severe reaction to the anticoagulant heparin. In patients taking heparin, this is called HIT, for heparin-induced thrombocytopenia.

Doctors investigating symptoms in the new COVID vaccine setting call it vaccine-induced thrombotic thrombocytopenia, or VITT.

The authors of the UK study found that the usual site of care test used to detect HIT – the HemosIL AcuStar HIT IgG test – was often negative for patients with VITT. They say VITT needs to be confirmed with a different type of test, ELISA or enzyme-linked immunosorbent assay.

Patients with VITT also need a different type of treatment than is usually given to people who experience dangerous blood clots or bleeding. Giving platelets, for example, to stop bleeding can make things worse. Instead, they require IVIG treatment to reduce obvious autoimmune attacks. Researchers say that, until more is known, it is also best to use an anticoagulant other than heparin to treat clotting.

Wherry said he wasn’t surprised to see some men affected, but so far, the emerging picture suggests women are at greater risk.

She said women tend to be more prone to autoimmune diseases and also more prone to blood clots due to these hormones. estrogen.

“So it fits this idea that this might 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 payments from one or more of the following companies: Bayer, Bristol Myers Squibb, Daiichi Sankyo, Pfizer, Novartis, Octapharma, Sanofi, Sobi, Alexion, and Takeda. Co-author of the grant report from Shire and Novartis; one of the authors reported another financial relationship with GSK; and a co-author reported on patent testing for bacterial meningitis based on a blood test, filed a patent pending decision.

Wherry reports consulting agreements with and / or is scientific advisor to Merck, Roche, Pieris, Elstar, and Surface Oncology. He has a PD1 patent licensing agreement with Roche / Genentech and is the founder of Arsenal Biosciences.

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