Risk of blood clots from COVID-19 higher than after vaccines: study

A The COVID-19 diagnosis is linked to a 39-in-1-million chance of developing a rare blood clot disease, compared to a 4-in-1-million chance after receiving the Pfizer or Moderna mRNA vaccines against the disease A data analysis carried out by researchers at Oxford University. The study, published on Wednesday (April 14), has not yet been peer-reviewed. The results add to concerns that discontinuing the use of other vaccines, namely the adenovirus-vector-based recordings from AstraZeneca and Johnson & Johnson, may not be worth the compromise of leaving people without protection against SARS-CoV-2.

Last month, some European countries stopped using the AstraZeneca prick due to concerns about blood clots. The European Medicines Agency later found that cerebral venous sinus thrombosis (CVST, also known as cerebral vein thrombosis or CVT) was an extremely rare side effect of the shot. Then, this week, U.S. health officials recommended a hiatus from Johnson & Johnson vaccinations after recipients were diagnosed with a handful of blood clots. Federal health authorities are investigating whether they are related to the vaccine.

For the new study, researchers used a database of electronic health records from patients who were primarily US residents to determine the risk of blood clots after vaccination against infection. Of the 513,284 COVID-19 patients identified in the database, 20 developed CVST within two weeks of their diagnosis. Two of 489,871 patients who received an mRNA vaccine developed CVST. As a control, researchers also analyzed the risk of developing CVST within two weeks of being diagnosed with flu, which was zero at 1 million.

The study finds that the European Medicines Agency’s latest estimate for the AstraZeneca vaccine-associated CVST risk is 5 per 1 million. The study did not look at the Johnson & Johnson vaccine.

“We have drawn two important conclusions,” says study co-author Paul Harrison CBS News. “First, COVID-19 significantly increases the risk of CVT and adds to the list of blood clotting problems that this infection causes. Second, the risk of COVID-19 is higher than current vaccines, even in those under the age of 30. This should be taken into account when considering the balance between risk and benefit for vaccination. ”

The study isn’t the first to link COVID-19 to an increased risk of blood clots. Aaron Petrey, an immunologist at the University of Utah who was not involved in the Oxford study, wrote in an email to The scientist For both COVID-19 and the vaccines, however, the risk appears to be linked to antibodies against a protein called anti-platelet factor 4. “I think the general conclusion from this article is correct and the risk of clots. . . is significantly higher in COVID because you have several mechanisms that all feed together and can lead to coagulopathy – from endothelial damage to platelet hyperreactivity to the cytokine storm associated with COVID-19, ”he writes. “There are a multitude of studies showing that COVID is a highly prothrombotic condition. As a result, thrombosis and stroke also occur in young healthy people who have mild symptoms after infection.”

See “The Specter of Endothelial Injury in COVID-19”

“I would say that the risk-benefit tradeoff is still strongly in favor of vaccination, although the authors in this article indicate that they did not compare the different risk-benefit ratios between vaccines,” adds Petrey.

Pfizer denies the study’s finding that mRNA vaccines were associated with a low risk of CVST, as stated in a statement emailed to The scientist“With over 200 million doses administered worldwide, Pfizer has performed a comprehensive assessment of the ongoing aggregate safety data for the Pfizer / BioNTech BNT162b2 vaccine that does not indicate that arterial or venous thromboembolic events, with or without thrombocytopenia, are a risk related to the Using our COVID-19 vaccine. “The statement noted that recent reviews by the US Centers for Disease Control and Prevention and the UK Medicines and Health Products Regulatory Agency also found no link between the Pfizer vaccine and blood clots.

Mary Cushman, a professor of medicine at the University of Vermont who specializes in hematology and was not involved in the study, says her results are consistent with the known association between COVID-19 and abnormal blood clotting disorders. But she warns in an email The scientist, “The authors of this work have made no adjustment for important risk factors for CVT or [venous thromboembolism] Like age, this can vary depending on the stakeholder group (COVID, influenza, Covid vaccine). Hence, it is difficult to fully interpret the results. “

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