Scientists in the US and UK believe they may have identified a key step 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 expected to become the workhorse of the global vaccination effort, thanks in part to promises to manufacture it on a non-profit basis during the pandemic and make it cheaply available in poorer countries. The company and its partners have distributed over two billion doses worldwide.
But reports of a rare side effect – an autoimmune response that in a small number of cases resulted in dangerous and sometimes fatal blood clotting – were among a series of setbacks that tarnished the vaccine’s reputation and forced many European countries to restrict its use. It has yet to receive approval in the United States, although the company 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 perhaps to develop new and improved vaccines to turn the tide of this global pandemic,” said Professor Alan Parker of Cardiff University School of Medicine. , one of the researchers who participated in the study, said in a press release.
The results, which were published Thursday in the journal Science Advances. it is believed that the problem is associated with the use of another harmless virus in the vaccine – adenovirus – to deliver the coronavirus gene into human cells in order to teach the immune system to recognize the virus and fight it.
The injection is injected into muscle tissue, but the report suggests that if the adenovirus enters the bloodstream, it can bind to a blood protein called platelet factor 4 or PF4, which is involved in the natural blood clotting process. In turn, in very rare cases, it can lead to the release of antibodies against the protein, causing platelet clustering and blood clots, the authors of the article say.
“With a better understanding of how PF4 and adenoviruses interact, it becomes possible to engineer the capsid or outer coat of the vaccine to prevent this interaction,” said Dr. Parker.
Johnson & Johnson’s vaccine also uses adenovirus, which is also associated with a rare bleeding disorder. Pfizer or Moderna shots are based on a different technology that does not use a helper virus.
Concerns about rare side effects first surfaced in March, prompting many European countries to rethink the use of the vaccine in some age groups.
The reaction was first discovered by scientists from Germany and Norway, but how and why it happened remained a mystery.
Public health experts have expressed concern that rare vaccine-related reactions have raised doubts, especially in Europe, and continue to stress that the benefits of the AstraZeneca vaccine far outweigh the risks.
In the UK, where the vaccine was first introduced in January, the National Health Service reports that “the risk of this extremely rare side effect is about 1 in every 100,000 first doses,” while the benefit of a single dose is associated with an 80% reduction in incidence. lethal outcomes. As of August 11, the side effect was linked to 73 deaths in the UK, according to the Medicines and Health Products Regulatory Agency. The UK has delivered over 25 million first doses of the vaccine.