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Recently, foreign media reported that researchers at the University of Frankfurt believe that they may have determined the cause of thrombosis after immunization with COVID-19 recombinant vector vaccines (such as AstraZeneca’s Vaxzevria and Janssen COVID-19 vaccines).
These rare coagulation events include cerebral venous sinus thrombosis (CVST) and visceral venous thrombosis (SVT) with thrombocytopenia (low platelets).
COVID-19 is a disease caused by the SARS-CoV-2 coronavirus.
In order to infect human cells, an extracellular protein called Spike (S) on the SARS-CoV-2 virus must interact with the angiotensin-converting enzyme 2 (ACE2) receptor expressed by certain human cells.
In response to this process, people have designed vaccines that enable the immune system to recognize and attack viruses that express the S protein.
For recombinant vector vaccines, this initiation is accomplished by using adenovirus vectors that do not cause disease in humans.
This adenovirus has been modified to transmit a copy of the genetic code required for the production of SARS-CoV-2 S protein to human cells.
These cells temporarily produce S protein through transcription and transport it to the outer membrane as a membrane-anchored protein.
The immune system then reacts to these proteins to produce immune memory.
According to preliminary studies, the rare coagulation events reported by these vaccines may be caused by the "vaccine-induced Covid-19 mimicry" syndrome (VIC19M syndrome).
Scientists have discovered that poor splicing events that occur after the transcription of S protein in human cells may cause the C-terminus of the protein to be truncated (shortened), resulting in soluble S protein being released into the blood and interacting with tissues that express ACE2 receptors.
Interactions with these tissues, especially vascular endothelial cells, may cause adverse side effects of blood coagulation, similar to those observed in patients with severe COVID-19.
The researchers also provided a possible explanation for why this coagulation occurred in recombinant vector vaccines rather than messenger RNA (mRNA) vaccines.
According to the researchers, the mRNA vaccine delivers mRNA molecules encoding the S protein directly to the muscle cells surrounding the injection site.
Cells that successfully absorb these nanoparticles will release their mRNA into the cytoplasm, where it will be translated into the S protein in the rough endoplasmic reticulum (ER).
After translation and folding, S protein undergoes post-translational modification in the endoplasmic reticulum and Golgi apparatus, and is transported to the outer membrane as a membrane-anchored protein.
However, they believe that when delivered through the adenovirus system, the adenovirus will enter the cell without being coated inside the cell, and then the adenovirus DNA will enter the nucleus and be transcribed into mRNA, producing proteins in the cytoplasm.
Scientists believe that post-transcriptional modifications in the nucleus of mRNA before it is transported and translated into protein may be the cause of the problem.
Reference source: Researchers may know the cause for COVID-19 vaccine related blood clotsReference source: Researchers may know the cause for COVID-19 vaccine related blood clots