The deadly blood clots linked to the AstraZeneca and Johnson & Johnson COVID-19 vaccines have raised great concern, but a group of scientists in Germany say they have figured out why this is happening.
The researchers suggest that vaccines that deliver adenovirus vectors – the cold viruses that are used to insert the spike protein of COVID-19 into the nucleus of the cell – can, in some people, cause pieces of the coronavirus proteins enter the nucleus and break apart.
The fragments then escape into the bloodstream and can cause clotting. Clots in the blood can then become serious if they get close to vital organs.
The scientists wrote in a pre-press study, which has not been peer-reviewed, that the vaccine is delivered into the nucleus of the cell and not into the surrounding fluid that acts as a protein factory.
“The life cycle of adenovirus includes infection of cells … entry of adenoviral DNA into the nucleus and, subsequently, transcription of genes by the host’s transcription machinery,” the researchers note.
“And precisely here lies the problem: the piece of viral DNA is not optimized to be transcribed within the nucleus.”
The Pfizer / BioNTech and Moderna vaccines are mRNA vaccines that do not use this system and no cases of blood clots have been reported at these doses.
However, scientists say that vaccine manufacturers can eliminate the risks.
Professor Rolf Marschalek, a professor at Goethe University in Frankfurt, who participated in the study, told the Financial Times that vaccines can be redesigned. He also told the newspaper that Johnson & Johnson is in contact with him.
Why do vaccines affect the very young?
The study suggests that older people use blood-thinning medications more often, or even daily, which could lower the risk of blood clots.
The researchers also suggested that the immune systems of older people show more immune senescence – the progressive decline in immune function with increasing age – meaning that young people show stronger immune reactions than older people, and older people women even stronger than men.
“All this would imply a higher incidence in young women compared to men or older people,” says the study.
The Oxford-AstraZeneca and Johnson & Johnson vaccines, in particular, have been linked to rare cases of fatal blood clotting disorders, especially in women under the age of 60.
What are the vaccine regulations in Europe?
The European Medicines Agency (EMA) said in April that there was a “possible link” between the AstraZeneca vaccine and “very rare cases of unusual blood clots with low platelets.”
The agency said it had received reports of 169 cases of this rare brain clot in early April, after 34 million doses had been administered in the European Economic Area (EEA).
But the EMA stresses that the benefits of getting vaccinated against COVID-19 outweigh the risks of developing blood clots.
Meanwhile, the UK has reported 309 clots and 56 deaths out of the 33 million vaccines given with AstraZeneca. And the Johnson & Johnson vaccine has been linked to 28 cases of clots in the United States.
As a consequence, some European countries temporarily suspended these vaccines, but have now set age limits. However, they have not reached a consensus on a common approach to managing them.
In Italy, the AstraZeneca vaccine is recommended for those over 60 years of age, in France those over 55 and in the United Kingdom it is discouraged for those under 30 years of age.