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Experts are learning more about the very rare blood clots people get after taking COVID-19 vaccines.
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The blood clots – called immune-thrombotic thrombocytopenia induced by vaccine – differ from other types.
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The CDC recommends different treatments and warns that treating VITT like other blood clots can be harmful.
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While scientists are investigating the rare blood clots that develop in a small number of people taking COVID-19 vaccines, they are learning that they differ in important ways from other blood clots.
It seems like the blood clots are taking place at most 5 people per million taking the shots. Researchers have given them a new name: immune thrombotic thrombocytopenia, or VITT, which is induced by vaccine.
They have a new challenge: to treat them in the same way that ordinary blood clots can be for patients, who can warn doctors of the Center for Disease Control and Prevention.
Experts believe that blood clots need a different approach because they tend to coexist with another symptom – lower platelet levels than usual.
Concerns about the specific new challenges that VITT presents are cited as a reason for the cautious approach of some regulators.
The disruption of the Johnson & Johnson vaccine in the US was in part to ‘prepare the healthcare system to recognize and treat patients appropriately’, said CDC’s deputy director, dr. Anne Schuchat, said in an information session on April 13.
According to the CDC, the use of standard blood clot treatments can be “harmful and alternative treatments should be given.”
The CDC, as well as medical bodies in the United Kingdom, have warned in particular against the use of the usual anticoagulant.
The combination of unusual blood clots with a low platelet count “in an otherwise healthy young individual is very unusual”, said Andreas Greinacher, a professor of transfusion medicine at the Greifswald University Clinic in Germany.
“It was the signal that caused all the suspicion and drove the vigilance of doctors to the problem.”
Greinacher spoke to Insider at a news conference on Friday about the clotting issue, which also provoked government reactions in Europe.
The European Medicines Agency has listed unusual low blood platelet counts as a very rare side effect of the AstraZeneca vaccine, which uses similar technology to Johnson & Johnson.
In the US, the CDC reported six cases of severe blood clots to the Johnson & Johnson vaccine, which asked the US to suspend its implementation.
The risk of developing VITT after vaccination remains extremely low. If we look at the number of cases detected compared to the millions of doses delivered, the risk between the AstraZeneca vaccine seems to be between 5 and a million.
It looks like it’s about 1 to a million for the Johnson & Johnson vaccine, although that’s a very rough estimate.
Regulators around the world agree that the benefits of COVID-19 vaccination outweigh the risks, although they have taken different approaches to deciding which groups to take which shots.
The decisions are complicated by the fact that the spread of COVID-19 in some countries is more intense than others, which changes the risk calculations.
The risks of getting COVID-19, including the risk of developing blood clots as part of the disease, are considered to be much higher than the risk of side effects of a COVID-19 vaccine.
39 cases of VITT have been reported in the New England Journal of Medicine. 40% of patients died.
It has low platelets and unusual blood clots in the brain, but also in the abdomen or liver. They all occurred in patients who had the AstraZeneca vaccine taken.
Greinacher was the lead author of an article published in the New England Journal of Medicine that described VITT in five cases from Germany and Austria.
Separately, another group, led by Professor Pål André Holme, chief physician at the University of Oslo in Norway, published similar conclusions for 11 patients there.
A UK study, published on April 16, led by Professor Marie Scully, Professor of Hemostasis and Thrombosis at University College London, shows another 23 cases of VITT after vaccination.
In almost every case, the patients developed anti-PF4 antibodies, which indicate that the body is attacking its own platelets. (PF4 is a chemical released by platelets.)
This is similar to another condition that scientists were already aware of called “heparin-induced thrombocytopenia” or HIT.
HIT rarely occurs in people taking heparin, a blood-thinning medicine. It is meant to disrupt the erasure process and help clear up any blockages.
In very rare cases, the body begins to attack the heparin. In more severe cases, the body becomes confused and also makes anti-PF4 antibodies to attack its own platelets.
It can therefore be dangerous to give heparin to patients with VITT, which results in new clues from regulators.
Professor Bruce Campbell, Head of Stroke and Interim Head of Neurology at Royal Melbourne Hospital in Australia, summed up the emerging consensus: ‘The recommendations made by expert bodies are to prevent us from using standard treatment for CVST , some heparin. “
(CVST stands for cerebral vascular blood clots, which means blood clots in the brain.)
There is still a lot of uncertainty: a formal link between the vaccine and VITT has not yet been established.
Scientists need time to thoroughly investigate the cases, which can be difficult because they are so rare. At the same time, regulators decide to act without absolute proof because the consequences can be serious.
For Holme, the Norwegian doctor, ‘nothing but the vaccine can explain why these individuals had this immune response’, reports The Wall Street Journal.
The mechanism behind this phenomenon is not clear at present. However, the New England editorial said in an editorial that to catch the syndrome earlier and learn how to treat it, it should reduce deaths due to VITT.
Asked if there was a greater risk of VITT for death, Campbell, the Melbourne neurologist, said: ‘I think there is not enough information at this stage to be confident about this.’
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