AstraZeneca: What's the deal with thrombosis?

Cerebral venous sinus thrombosis led to a halt to Astrazeneca's vaccine in many countries. But what exactly are these thromboses? And was the emergency halt of the vaccine too hasty?

For safety reasons, vaccination with the Oxford vaccine from AstraZeneca has been suspended in many countries until further notice. For Germany, this decision was made on March 15 by Health Minister Jens Spahn.

Why? Seven cases of a rare thrombosis, all within a short time of vaccination, had been reported to Germany's vaccine regulatory authority, the PaulEhrlich-Institute (PEI). Three of them ended fatally for those affected.

This is what is known so far about the connection between the vaccine and thrombosis.

Blood clotting in the brain: What exactly was observed?

So far, seven cases of socalled Cerebral venous sinus thrombosis (CVST) have occurred in 1.6 million people vaccinated with AstraZeneca. At the same time, the affected individuals were also found to be deficient in platelets, which can affect blood clotting.

In CVST, a blood clot clogs the veins in the brain that are normally the route oxygen-depleted blood takes to drain to the heart. However, if the blood can no longer drain properly, the pressure in the brain increases and further bleeding can occur there. In the worst case, CVST leads to fatal strokes.

However, this type of thrombosis is considered rather rare, looking at its incidence: It is estimated that two to five people per 1 million experience CVST over the course of a year. However, recent studies indicate a higher number of people affected. As many as 15.7 cases per million people per year have been reported in an Australian study, says Paul Hunter, professor of medicine at the University of East Anglia. That would mean the current incidence is underestimated by four to eight times, according to Hunter.

Does thrombosis always equal thrombosis?

Since the announcement of the vaccination suspension, there has been much discussion. Especially on social media, there were many angry responses: Why is the contraception pill still prescribed, even though it is known that roughly 1,100 women will suffer thrombosis among every 1 million who take it. In comparison: Why do authorities throw the entire vaccination strategy out the window after only seven cases of thrombosis in 1.6 million vaccinated people?

SPD health expert Karl Lauterbach criticized this comparison in an interview with German public radio Deutschlandfunk. CVST is not comparable in severity to thromboses caused by the pill, he argued.

When people talk about thrombosis in connection with the contraceptive pill, they are usually referring to leg vein thrombosis. In this case, blood clots clog the veins in the legs and, if they break loose, can travel to the lungs and cause an embolism.

But that is not the entire truth: Taking the pill also increases the risk of the more dangerous CVST. "Women are affected more often than men, and hormones probably play a role. In late pregnancy, in the puerperium and in women taking the contraceptive pill, we see CVST most frequently," Peter Berlit, secretary-general of the German Society for Neurology, told DW. Regardless of gender, younger people are generally affected more often than older people, he said.

Is the vaccination pause justified?

Spahn's decision to pause vaccine distribution is, of course, no coincidence. He is referring to a recommendation by the PEI, which tests vaccines and medicines for safety in Germany. And the PEI said in a press release that it "recommends the temporary suspension of vaccinations with the COVID-19 vaccine AstraZeneca after intensive consultations on the serious thrombotic events that have occurred in Germany and Europe."

Lauterbach said in the Deutschlandfunk interview that he thought a link between the vaccination and the thrombosis cases was quite likely. Nevertheless, in his opinion, that was not a good enough reason to suspend the vaccinations: "I would not have decided it that way based on the same data," he continued.

Berlit, who teaches at the University of Duisburg-Essen, also has a hard time with the authorities' decision. "At the moment, from a purely statistical point of view, there are more arguments against a connection than for a connection."

Thus, the current number of cases would still be in the range of the previously known incidence for CVST without vaccinations.

There's still a problem with the comparison, though: Typically, statisticians look at CVST over a full year. The cases associated with vaccinations, however, have all occurred since February of this year. But Berlit has a possible explanation for this, too. "It is known that CVST can also occur frequently in connection with infections. Of course, infections occur more frequently in the seasons of weather change, such as spring and fall. And therefore CVST are also more frequent," he explains.

Researchers have long observed that COVID-19 infections, for example, also lead to more frequent thrombosis. This is presumably due to the fact that in the case of COVID-19, our immune system upregulates a certain defense mechanism that

influences blood clotting and can thus lead to more thromboses.

Vaccination strategy: Which decision is the right one?

Berlit considers speculation that active ingredients in the vaccine could trigger thrombosis in a similar way to COVID-19 to be speculative. "This is all hypothetical. So far, there are no indications of this. This accumulation has so far only occurred in Germany and not, for example, in England," he says.

The British are largely unimpressed by the current developments — with vaccinations continuing there. With 11 million doses administered, only three people have been reported as experiencing CVST.

Hunter, of the University of East Anglia, argues that a possible link needs to be investigated more closely. But he adds that one should also consider the real harm that could be done by delaying vaccination in the face of rising infection rates in Europe.

The European Medicines Agency (EMA) is currently investigating the reported cases in more detail. However, it too sees no reason for AstraZeneca to pause just yet. While its investigations are ongoing, the EMA stated that the benefits of AstraZeneca's vaccine in containing COVID-19 and its associated risks outweigh the side effects. Results are expected within the next two weeks.

"Whether it's the right decision to completely stop giving the vaccine now for the time being, that's more of a political discussion now," Berlit says. "I think the risk of serious neurological complications from COVID-19 infection is statistically higher than from vaccination. Actually, all the data point in that direction."

What should vaccinated individuals be aware of?

Those who have already received vaccination with AstraZeneca's vaccine should watch out for the following symptoms, according to Berlit: "People who have persistent and very severe headaches within the first 2-3 weeks after vaccination need to get further evaluation." Similarly, pinpoint-shaped hemorrhages in the skin along with the headache may indicate CVST.

That's how a thrombosis looks in a CT