An international team of researchers has finally revealed the scientific reason behind the rare blood clots that appeared in some recipients of adenovirus-based coronavirus vaccines.
Since the emergence of coronavirus vaccines, very rare cases have been recorded of people suffering from serious blood clots after receiving some vaccines, but no one has been able to explain the reason precisely.
Today, researchers from Canada, Australia, and Germany have uncovered the mechanism that leads to these rare strokes, revealing that the problem begins with a simple but catastrophic mistake made by the immune system.
In very rare cases, the immune system mistakenly identifies its target and attacks the body's own cells instead of defending it.
The new study details how the body can sometimes produce harmful antibodies that attack normal blood proteins, leading to a condition known as "vaccine-induced thrombocytopenia and immune thrombosis." The research team was able to identify the precise viral component responsible for triggering this response.
How does the problem occur?
Imagine your immune system as a trained army protecting the body from enemies. When an adenovirus enters the body, whether through natural infection or vaccination, this army begins producing special weapons called "antibodies" to counter a specific protein in the virus called "protein VII".
The problem is that this viral protein is very similar to a natural human protein called platelet factor 4. In the vast majority of people, this similarity does not cause any problem, because the immune system accurately distinguishes between them.
However, in very rare cases, during the ongoing battle between the immune system and the virus, a minor genetic mutation occurs in a single antibody-producing cell. This mutation alters only one amino acid out of the thousands that make up that cell.
Despite its simplicity, this small change is sufficient to redirect the antibody's focus from the viral protein to the human protein.
When this mutated antibody binds to the human protein, it abnormally activates platelets, leading to blood clots and a decrease in the number of platelets, which is the hallmark of this rare condition.
Most importantly, the researchers found the exact same mutation in every antibody they analyzed from patients who had suffered these blood clots. Not only that, but they engineered antibodies in the lab and reversed this mutation, completely eliminating their ability to cause clotting. This is conclusive evidence that this mutation is the primary cause of this condition.
"This discovery shows, with molecular precision, how a normal immune response can go awry in very rare cases," says Theodore Warkenten, professor emeritus at McMaster University in Canada and lead author of the study. "For the first time, we not only understand what is happening, but we understand why it is happening
This single discovery answers five questions that have remained unanswered for years:
Why can adenovirus vaccines and natural infection cause this condition?: Because both expose the body to viral protein that is similar to human protein.
Why does the body specifically target the human protein "platelet factor 4"?: Because of the great similarity between it and the viral protein.
Why is this condition so rare? Because it only occurs if three conditions are met together: exposure to the virus, the presence of the appropriate genetic predisposition, and the occurrence of a random mutation in the immune cell.
Why does the incidence rate vary between population groups? Because the gene associated with this condition is more common in people of European descent
Why did so many cases occur after the first dose of the vaccine? Because the body had already developed initial immunity against the viral protein, and upon re-exposure, the immune response is amplified.
What is encouraging is that this discovery not only explains a medical mystery but also opens the door to developing safer vaccines in the future. Now that scientists know exactly which part of the virus is responsible for this problem, they can redesign vaccines to retain their effectiveness while avoiding this rare immune response
