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Experts are learning more about the very rare clots that some people receive after receiving COVID-19 vaccines.
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The clots – called vaccine-induced thrombotic immune thrombocytopenia – differ from other types.
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The CDC recommends various treatments, warning that treating VITT like other clots can be harmful.
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As scientists investigate the rare blood clots that develop in a small number of people taking COVID-19 vaccines, they learn that they differ from other clots in crucial ways.
Clots appear to occur in up to 5 people in a million who catch fire. The researchers gave them a new name: vaccine-induced immune thrombotic thrombocytopenia or VITT.
These come with a new special challenge: treating them in the same way as more common clots can be bad for patients, resulting in warnings to doctors at the Centers for Disease Control and Prevention.
Experts believe that clots need a different approach, because they tend to occur with another symptom – lower than usual levels of platelets in the blood.
Concerns about the new specific challenges posed by VITT have been cited as a precautionary approach by regulators.
The discontinuation of the Johnson & Johnson vaccine in the United States was partly “preparing the health care system to recognize and treat patients properly” when clots appear, CDC Deputy Director Dr. Anne Schuchat said in an April 13 briefing.
According to the CDC, the use of standard treatments for blood clots “can be harmful and alternative treatments must be given.”
The CDC, as well as medical bodies in the UK, have specifically warned against the use of the common anti-coagulation drug herapin.
The combination of unusual blood clots with low platelet counts “is very unusual in an otherwise healthy young person,” said Andreas Greinacher, a professor of transfusion medicine at the Greifswald University Clinic in Germany.
This was the signal that raised all suspicions and led the vigilance of doctors to this problem.
Greinacher spoke with Insider on Friday in a news briefing on the clotting problem, which also provoked regulatory responses in Europe.
The European Medicines Agency has listed unusual blood clots with low platelets as a very rare adverse event of the AstraZeneca vaccine, which uses a technology similar to that of Johnson & Johnson.
In the US, the CDC reported six cases of severe clots after the Johnson & Johnson vaccine, prompting the US to discontinue its launch.
The risk of developing VITT after vaccination remains extremely low. Regarding the number of cases detected compared to the millions of doses administered, the risk seems to be 5 to one million for the AstraZeneca vaccine.
It appears to be about 1 to one million for the Johnson & Johnson vaccine, although this is a very crude estimate.
Regulators around the world agree that the benefits of COVID-19 vaccination far outweigh its risks, although they have taken different approaches to deciding which groups should take what blows.
Decisions are complicated by the spread of COVID-19 being more intense in some countries than in others, changing risk calculations.
The risks of taking COVID-19, including the risk of developing blood clots as part of this disease, is considered to be much higher than the risk of adverse events from a COVID-19 vaccine.
39 cases of VITT have been reported in the New England Journal of Medicine. 40% of these patients died.
They had low platelets and unusual blood clots in the brain, but also in the abdomen or liver. All occurred in patients receiving a single injection of AstraZeneca vaccine.
Greinacher was the lead author of a paper published in the New England Journal of Medicine describing VITT in five cases in Germany and Austria.
Separately, another group, led by Professor Pål André Holme, chief physician at the University of Oslo in Norway, published similar findings for 11 patients there.
A study in the UK published on April 16, led by Professor Marie Scully, a professor of hemostasis and thrombosis at University College London, showed another 23 cases of VITT after vaccination.
In almost every case, patients have developed what are called anti-PF4 antibodies, a response that suggests that the body is attacking its own platelets. (PF4 is a platelet-releasing chemical.)
This is similar to another condition that scientists were already aware of “heparin-induced thrombocytopenia” or HIT.
HIT occurs in rare cases in people who are given heparin, a medicine that dilutes the blood. It is meant to interrupt the deletion process and help remove any blockages.
In very rare cases, the body begins to attack heparin. In more severe cases, the body becomes confused and also produces anti-PF4 antibodies to attack its own platelets.
This is why the administration of heparin to patients with VITT could be dangerous, leading to new guidance from regulators.
Summarizing the emerging consensus, Professor Bruce Campbell, Head of Stroke and Acting Head of the Department of Neurology at Royal Melbourne Hospital in Australia, told Insider: “The recommendations made by the expert bodies are to avoid using our standard treatment for CVST, which is heparin “.
(CVST means cerebral vascular blood clots, which means blood clots on the brain.)
A lot of uncertainty remains: no formal link has been established between the vaccine and VITT.
Scientists need time to look closely at cases, which can be difficult because they are so rare. At the same time, regulators decide to act without absolute evidence, as the consequences can be serious.
For Holme, the Norwegian doctor, however, “nothing but the vaccine can explain why these individuals had this immune response,” the Wall Street Journal reported.
The mechanism behind this phenomenon is unclear at this time. However, catching the syndrome earlier and learning how to treat it should reduce VITT mortality, New England editors said in an editorial.
Asked if there was a higher risk of death from VITT, Melbourne neurologist Campbell said: “I don’t think there is enough information at this stage to be confident about that.”
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