When do rare blood clots appear after receiving the AstraZeneca vaccine?

The European Medicines Agency confirmed on Wednesday that “no causal link (with the vaccine) has been proven, but it is possible and further analysis is underway.” The agency will meet again to consider the matter between April 6-9.
But other specialists from all over Europe issued more categorical opinions.
André Holme, an official at the Oslo National Hospital who works on these cases, said in a statement to Norwegian television TV2 on March 27 that “we must stop speculating on whether there is an association or not.” All cases developed symptoms three to ten days after receiving the AstraZeneca vaccine. We did not find any other causal factors. “
“The Norwegian Medicines Agency estimates that there is a possible link to the vaccine,” Norwegian health official Steinar Madsen told AFP.
The French Medicines Agency confirmed on March 26 that it was a “rare” possibility, based on “the atypical nature of these clots, their similar clinical symptoms and the near time of their appearance.”
How big is the threat?

This is the basic question. According to figures published this Wednesday by the European Medicines Agency, so far 62 cases of cerebral venous thrombosis have been recorded in the world, 44 of them in 30 countries of the European Economic Area (European Union, Iceland, Norway and Liechtenstein) of 9.2 million doses of vaccine used.
14 deaths have been recorded, not always reliably attributed to atypical strokes, IAEA Director Amir Cook said Wednesday during an online news conference.
The agency clarified that these data are partial.
Germany has registered 31 suspected cases of cerebral venous thrombosis (19 of them with low platelet counts) and nine deaths, according to the Paul Ehrlich Institute.
This represents an average of 1 case per 100,000 doses of AstraZeneca (2.8 million doses have been used).
Cases have also been reported in France (12, including four deaths, of 1.9 million doses, according to the French Medicines Agency), in Norway (five cases, including three deaths, of 120,000 doses), as well as in the countries Low. .
In the UK, which uses the AstraZeneca vaccine on a large scale, 30 cases, including seven deaths, were reported out of 18.1 million doses used.
But as with any drug, knowing the risks is not enough, as it must be weighed against the benefits the product provides.
The European Medicines Agency, on Wednesday, reiterated its position on March 18 after monitoring the first cases, and said that “the benefits of the AstraZeneca vaccine in preventing Covid-19, which leads to hospitalizations and deaths, exceed those risks of side effects “. “
Are there risk factors?

So far, the majority of cases have occurred in people under the age of 65, most of whom are women. However, no conclusion can be drawn from this, because it may be the result of vaccinating young people with it mainly at the beginning of vaccination campaigns.
In addition, the high percentage of women among the reported cases may be related to the frequent use of the vaccine in the vaccination of health personnel, which is a priority group, and the presence of women among them is more frequent.
The European Medicines Agency believes that “so far, tests have not identified any specific risk factors for these rare diseases, such as age, gender or medical history, including blood clotting problems.”
However, after the first wave of suspension of the use of the vaccine in mid-March, some countries decided not to administer this vaccine to people under a certain age.
Germany is the latest country to decide on Tuesday to restrict use of the vaccine for those under the age of 60, while Canada suspended its use for those under the age of 55. They were preceded by France (55 years), Sweden and Finland (65 years).
“We don’t have just one vaccine, but several,” said Sandra Sissek, a virologist at Goethe University in Frankfurt. “That’s why it makes sense to me that assigning AstraZeneca to the elderly makes sense to me.”
Norway and Denmark have taken a more drastic option by completely suspending the use of the AstraZeneca vaccine for now.
– What are the reasons?

We are still in the hypothesis stage and this is one of the points that the European Medicines Agency must clarify.
In a study published online on March 28, which has yet to be evaluated by other scientists, German and Austrian researchers compared the issue to another known phenomenon.
The researchers, led by Andreas Grinscher (University of Greifswald), said that the phenomenon associated with the AstraZeneca vaccine “is clinically similar to the platelet weakening of heparin.”
Platelet dysfunction due to heparin is a rare, severe, and abnormal immune reaction that occurs in some patients when receiving the anticoagulant drug heparin.
A team from the National Hospital in Oslo estimated on March 18 that these cases could be interpreted as a result of a “strong immune response” to the vaccine.
In turn, the association of French doctors and researchers called “Ducoti de La Lions” (in science class) considers that the cases are caused by a “severe immune reaction”, and proposes an innovative hypothesis.
The group believes that the starting point could be the “accidental injection of the vaccine into a vein in the deltoid muscle” (in the shoulder).
He adds in a post on his website that “in the presence of factors that have not been fully identified,” “an accidental intravenous injection (…) would generate a differentiated immune reaction.”