Canadian study shows success of treatment for blood clots connected with AstraZeneca’s COVID-19 vaccination


With more than 80 percent of the world’s population still vulnerable against COVID-19, a team of Canadian researchers has documented a successful treatment for blood clots associated with the Oxford-AstraZeneca vaccine, a global effort to combat the pandemic. is an important weapon.

The results provide confidence that the clot can be arrested if caught in time. However, they do not completely eliminate the potential for death or serious complications related to the rare condition known as vaccine-induced immune thrombotic thrombocytopenia, or VITT.

In a study published Wednesday in the New England Journal of Medicine, a team led by researchers at McMaster University in Hamilton, Ont. reports on treatment for three Canadian patients who developed VITT. Each patient received a combined therapy consisting of antibodies delivered intravenously with anticoagulants.

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Ishaq Nazi, scientific director of McMaster’s Platelet Immunology Laboratory, said while the approach has already been used, the Canadian case series shows both the effectiveness of the therapy and why it can prevent the formation of blood clots after vaccination. -Author on the study.

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Dr. Nazee said he and his colleagues have seen similar results in other patients, but only three were included in the study to expedite publication.

“We wanted to get it out as soon as possible so that doctors could know how it’s working and what to look out for,” Dr. Nazi said.

Analysis of the patients showed that the antibodies they received as part of their treatment were able to knock out a distinct population of “VITT antibodies” that developed in response to the vaccine. It is the VITT antibodies that form complexes that can bind to clotting factors in the bloodstream and activate platelets. This releases more clotting factors, triggering a cascade that leads directly to VITT. Antibody therapy was shown to block that process, although it did not directly eliminate VITT antibodies from patients.

McMaster researcher and hematologist Ted Warkentin, who participated in the study, said the results provide new information about life-saving treatments. He said that one of the patients suffered severe trauma and the other had to amputate part of a leg as a result of VITT, demonstrating the dire consequences that could arise for some people who developed the rare condition.

“It is worrying that two out of three patients had life-changing clots,” said Dr. Warkentin said.

The study also found that one in three patients had a recurrence and was switched to a different therapy.

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Researchers have yet to work out exactly what it is about the AstraZeneca vaccine — and to a lesser extent the one-dose vaccine made by Johnson & Johnson — that triggers VITT, or why it is so rare.

Since March, more than 2.2 million Canadians have received the AstraZeneca vaccine or its made in India equivalent, according to Health Canada data. Among them, about 40 individuals developed symptoms of VITT within 3 to 34 days after vaccination. As of May 28, five of those cases have resulted in death.

This rate reflects a roughly 1-in-50,000 chance of developing VITT seen in other countries. While the risk remains low, especially when compared to the risks associated with COVID-19, it proved enough to turn many Canadians away from the AstraZeneca vaccine when a large number of alternatives began to arrive last month. Until then, the National Advisory Committee on Immunization had designated mRNA vaccines made by Pfizer-BioNtech and Moderna as the preferred option if they were already available.

The question is where does this leave the rest of the world, especially in countries that lack the resources to buy an mRNA vaccine.

“Not every country has that luxury right now,” said Ben Chan, a physician and assistant professor at the University of Toronto’s Institute for Health Policy, Management and Evaluation.

The challenge, he adds, is that laboratory tests that can identify VITT, MRI scans that spot blood clots and specialists who can provide antibody therapy are also luxuries that are hard to come by in many parts of the world , especially where the AstraZeneca vaccine may be used to the best effect.

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“We have to be realistic about whether low- and middle-income countries will have the resources to diagnose and treat VITT early,” Dr. Chan said.

He said a very positive development is that the rare syndrome was discovered and within a few weeks an effective treatment was developed. “In my 31 years as a physician, I have never seen science develop so rapidly,” he said.

Paul Petrasek, a vascular surgeon and an associate professor at the University of Calgary, said Canadian physicians now know better about VITT than it was known in early April, when they first encountered a 63-year-old male patient. Event.

“We were initially misled because of some of the initial data coming from Europe,” said Dr. Petrasek.

Those data suggest that VITT was primarily an issue in younger women. This will become an artifact due to the fact that front-line health care workers are among the first to receive the AstraZeneca vaccine, a demographic group dominated by that.

Dr. Petrasek said it took an additional two days to identify what his patient was experiencing. The case is one of three documents recorded in the McMaster study.

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