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Study suggests link between AstraZeneca vaccine and blood clots

Scientists in the United States and Britain believe they have identified a key milestone in how the Covid vaccine developed by AstraZeneca and the University of Oxford can cause an extremely rare but serious blood clotting disorder.

The AstraZeneca vaccine was to be the backbone of vaccination efforts around the world, in part thanks to promises to manufacture it nonprofit during the pandemic and make it available cheaply in the poorest countries. The company and its partners have distributed more than two billion doses around the world.

But reports of the rare side effect – an autoimmune response that has led to dangerous and sometimes fatal clotting in a small number of cases – were part of a series of setbacks that have tarnished the vaccine’s reputation and spurred many European countries to limit its use. It has yet to receive clearance in the United States, although the company has said it hopes to get approval soon.

“We hope our findings can be used to better understand the rare side effects of these new vaccines – and potentially to design new and improved vaccines to turn the tide of this global pandemic,” said Professor Alan Parker of the Faculty of Cardiff University medicine, one of the researchers involved in the study, said in a press release.

The results, which were published Thursday, in the journal Science Advances. suggest that the problem is related to the vaccine’s use of another harmless virus – an adenovirus – to introduce a coronavirus gene into human cells to train the immune system to recognize and fight the virus.

The vaccine is injected into muscle tissue, but the report suggests that if the adenovirus gets into the bloodstream, it can bind to a protein in the blood called platelet factor 4, or PF4, which is involved in the process. natural coagulation. This process, in turn, could lead to the release of antibodies against the protein, causing platelets to aggregate and blood clots to form in very rare cases, the article’s authors said.

“With a better understanding of the mechanism by which PF4 and adenoviruses interact, it is possible to design the capsid, or outer envelope of the vaccine, to prevent this interaction from occurring,” said Dr. Parker.

The Johnson & Johnson vaccine also uses an adenovirus and has also been linked to the rare blood clotting disorder. The Pfizer or Moderna plans are based on a different technology, which does not involve a helper virus.

Concerns about the rare side effect first surfaced in March, prompting many European countries to rethink the use of the vaccine in certain age groups.

The reaction was first discovered by scientists in Germany and Norway, but how or why it happened has remained a mystery.

Public health experts have expressed concern that the rare vaccine-related reactions have fueled reluctance, especially in Europe, and continue to stress that the benefits of the AstraZeneca vaccine far outweigh the risks.

In Britain, where the vaccine was first used in January, the National Health Service reports that “the risk of this extremely rare side effect is around 1 in 100,000 first doses” while the benefit of one dose results in an 80 percent reduction in deaths. As of August 11, the side effect was linked to 73 deaths in Britain, according to the country’s Medicines and Health Products Regulatory Agency. Britain has administered more than 25 million first doses of the vaccine.

nytimes Gt

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