How concerned should we be about the association of blood clots with AstraZeneca’s vaccine?


© Reuters. COVID-19 vaccinations in Madrid


By John Miller and Ludwig Burger

ZURICH (Reuters) – Europe’s Medicines Agency on Wednesday found a possible link between AstraZeneca’s (NASDAQ 🙂 COVID-19 vaccine and very rare blood clots in adults who received the shot. The UK recommended that people under 30 get an alternative COVID-19 vaccine if possible.

We know the following so far:


The EMA said that by April 4, its vaccine side effect monitoring system had received 169 reports of cerebral venous sinus thrombosis (CVST) or blood clots in blood vessels emerging from the brain, and 53 cases of splanchnic vein thrombosis (SVT). or clotting in veins in the abdomen.

This equates to approximately 34 million AstraZeneca vaccine doses administered in the UK and the European Economic Area since vaccination began almost three months ago.

His safety committee conducted a review of 62 cases of CVST and 24 cases of SVT, of which 18 were fatal.

Most of the reported cases occurred in women under the age of 60, although this could be misleading. Germany and the UK say far more women have received AstraZeneca’s shot than men.

Most cases occurred within 2 weeks of receiving the first dose.

German vaccination officials who recorded 29 cases of CVST in women aged 20 to 59 who received the AstraZeneca vaccine said the incidence rate in this group was 20 times higher than normally expected within 16 days of vaccination.

The German Ministry of Health stated that 1 to 1.4 cases of CVST would have been expected during this time.


The Medicines and Health Products Regulator looked at 79 cases of rare coagulation associated with low platelets, with 19 deaths – 13 women and 6 men. Eleven of the deaths among people under the age of 50 and three under the age of 30.

All 79 cases occurred after a first dose of the vaccine.


British officials relied on statistics from the University of Cambridge’s Winton Center for Risk and Evidence Communication to explain their recommendations that young people get an alternate shot while older people are still given AstraZenecas.

According to the center, vaccination with the AstraZeneca shot would reduce ICU admissions by nearly seven out of 100,000 people in the group aged 20 to 29 at high risk of exposure to the virus, while 1.1 people per 100,000 people in Living in the Same Group The group has been estimated to suffer serious vaccine-related harm.

The risk of serious harm from vaccinations continues to decrease the older people get, and admissions to the intensive care unit prevented by vaccinations increase sharply, increasing the risk-benefit ratio of the AstraZeneca shot. The center concluded that only 0.4 people per 100,000 in the 50 to 59 age group would experience vaccine harm, while 95.6 intensive care admissions per 100,000 would be prevented.

EMA investigators checked whether the incidence of events in the vaccinated population was higher than normal background rates obtained from public health statistics or insurance records. This would be combined with a medical analysis of each individual case and findings from the scientific literature.

In its findings on March 18, the EMA said that people under the age of 50 could expect an average of just 1.35 cases of CVST within 14 days of receiving the vaccine from AstraZeneca, while 12 cases had been recorded on the same reference date.

For comparison: four out of 10,000 women would get a blood clot using oral contraception.

Key to the EMA’s assessment that the benefits continue to outweigh the risk are its conclusions on the likelihood of an increased risk of clotting compared to the benefits of preventing COVID-19 and reducing hospital stays and deaths.


The EMA said unusual blood clots with low platelets should be listed as a very rare side effect and countries should decide how to proceed with their national COVID-19 vaccination campaigns.

These can vary from country to country, the EMA said, depending on factors like the spread of infections and vaccine availability. The safety committee requested new studies and changes to ongoing ones to get more information about the mechanism behind the rare clots.

AstraZeneca and European regulators have stated that no blood disease concerns have been identified during clinical trials.

Are there any theories as to what could lead to the clots?

One of the possible causes for these rare blood clot veins to be investigated is that, on rare occasions, the vaccine raises an unusual antibody.

The EMA said the vaccine could trigger an immune response that leads to abnormal clotting, although it acknowledged that scientists have not yet identified any risk factors that could predispose someone to clotting when combined with low platelets.

German scientists at the University of Greifswald came to the conclusion that the vaccine is related to the side effects, although their work still requires peer review. Andreas Greinacher, an expert on drug-induced immune responses, said the samples he examined showed unusual antibodies that activate platelets and trigger the clots.

Greinacher is still looking for clues as to why some people had clots and others didn’t.

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