AstraZeneca vaccine doubles incidence of cerebral venous thrombosis


Two independent teams of British scientists have found that vaccination with the coronavirus drug AstraZeneca increases the incidence of cerebral venous thrombosis by about twice as much as pre-vaccination values. The researchers calculated that vaccination causes 1 to 3 excess cases per million people. Both the first and second papers were published in PLOS Medicine.

AstraZeneca was found to have side effects

A few months after the AstraZeneca coronavirus vaccine began being used in Europe, it was found to have side effects. One of these was thrombosis, which rarely, but still affected young women. After discovering this adverse reaction, the European regulator listed thrombosis as a rare side effect of the AstraZeneca drug in April 2021.

Researchers then found out why the vaccine triggers the clotting process. It turned out that adenovirus, which is used as a vector in the vaccine, can bind to the platelet-derived cytokine PF4. The immune system then confuses PF4 with the foreign adenovirus and produces antibodies against it, which causes thrombosis. Scientists have agreed that this condition resembles the well-known heparin-induced thrombocytopenia in its mechanisms.

So far, there have been no studies on large samples examining the incidence of thrombosis after vaccination. Two articles have now been published simultaneously in which the incidence of thrombosis after vaccines was analyzed in a large sample of British residents.

In the first study, physicians led by William N. Whiteley of the University of Edinburgh used data from 46 million Britons, 21 million of whom were vaccinated with AstraZeneca and Pfizer. Researchers compared the number of thromboses in vaccinated and unvaccinated people using information from electronic health records from Dec. 8, 2020, through March 18, 2021. They found that among people over age 70, vaccination was not associated with an increased risk of thrombosis, but among people under age 70, those vaccinated with AstraZeneca had a slightly higher risk of cerebral venous thrombosis (aHR = 2.27) than those unvaccinated. This corresponds to 0.9 to 3 excess cases per million people, which is about twice as high as in the unvaccinated.

In the second study, health professionals led by Steven Kerr of the University of Edinburgh followed 11.6 million people in England, Scotland and Wales. Researchers compared the incidence of cerebral sinus thrombosis up to three months before vaccination with AstraZeneca and Pfizer and one month after the first dose of vaccine. The data were taken from national medical databases for the period December 8, 2020, through June 30, 2021. The medics got similar results to their counterparts. After AstraZeneca administration, the rate of cerebral sinus thrombosis increased about twice as much as before vaccination. This corresponds to one additional case per 4 million vaccinated people.

It is worth noting that both studies found no association between vaccination with Pfizer and thrombotic complications.

We recently reported on a study in which British medical professionals looked at patients’ electronic medical records, trying to understand how common post-vaccination and covid thrombosis were. They estimated that the risk of thrombotic complications after COVID-19 was about eight times higher compared to the condition after vaccination.

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