AstraZeneca and Johnson & Johnson jabs have caused rare blood clots but scientists say they can be redesigned to avoid problem

The AstraZeneca coronavirus vaccine.There have been 309 cases of blood clots in the UK out of 33 million people given the AstraZeneca vaccine.Photograph: Alastair Grant/AP



A team of German scientists believe that they have worked out why some people given the AstraZeneca and Johnson & Johnson vaccines against Covid-19 develop blood clots – and claim they can tell the manufacturers how to improve the vaccine to avoid it.

The key is in the adenovirus – the common cold virus that is used to deliver the spike protein of the coronavirus into the body, say Rolf Marschalek, a professor at Goethe university in Frankfurt, and colleagues. The mRNA vaccines developed by Pfizer/BioNTech and Moderna do not use this delivery system and there have been no blood clotting cases linked to them.

The blood clots are rare but troubling in the younger age group who are more at risk of clotting and less likely to experience severe Covid illness. The UK is now offering anyone under the age of 40 a choice of vaccines, where available. There have been 309 cases in the UK out of 33 million people given the AstraZeneca vaccine.

The scientists in a pre-print which has not undergone peer review say they believe the problem lies in the entry of the adenovirus into the nucleus of the cell rather than the just the cellular fluid, where the virus normally makes proteins.

“The adenovirus life cycle includes the infection of cells … entry of the adenoviral DNA into the nucleus, and subsequently gene transcription by the host transcription machinery,” they write.