German scientists claim to have discovered why some coronavirus vaccines cause blood clots.
The researchers said Covid-19 vaccines that employ adenovirus vectors - cold viruses used to deliver vaccine material - send some of their payload into the nucleus of cells.
Some of the instructions for making coronavirus proteins can be misread, potentially triggering blood clot disorders in a small number of recipients, they suggest.
Johnson & Johnson and the AstraZeneca have been linked to rare, but serious, blood clots over the last few months. This has led some countries such as Denmark, Norway and Austria, to cease the use of the jab while others restricted its use to older adults.
In the UK the AstraZeneca vaccine has been linked to 309 clotting cases and 56 deaths out of 33 million shots.
Dr Rolf Marschalek, a professor at Goethe University who led the study, believes that after entering the nucleus, parts of the spike protein splice or split apart and create mutant versions which are unable to bind to the cell membrane.
These then enter the body and trigger the rare blood clots.
Marschalek told the Financial Times that the process is different with mRNA vaccines, such as those made by Pfizer and Moderna, because the genetic material of the spike protein is sent directly to the cell fluid and does not enter the nucleus.
The paper, which has not yet been reviewed by experts, also suggests that those making vaccines using adenovirus vectors could alter the sequence of the spike protein “to avoid unintended splice reactions and to increase the safety of these pharmaceutical products.”
Johnson & Johnson, in an emailed statement to Reuters, said: “We are supporting continued research and analysis of this rare event as we work with medical experts and global health authorities. We look forward to reviewing and sharing data as it becomes available.”
AstraZeneca declined to comment.
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