Mar.18 -- The European Medicines Agency said AstraZeneca Plc’s Covid-19 vaccine is safe to use after several European nations suspended use of the shots over concerns about blood clots. EMA Executive Director Emer Cooke speaks at a press conference
Two teams of European scientists, working independently, say they believe they've identified the cause of a rare blood clotting condition that has occurred in some people after receiving the AstraZeneca COVID-19 vaccine.
If correct, their research could mean any blood clots that occur could be easily treated.
There were reports earlier this month of roughly 30 blood clots occurring after vaccination, a few of them fatal. This led more than a dozen European countries to suspend their use of the AstraZeneca vaccine.
Most countries resumed using it, however, after the European Medicines Agency conducted an investigation and declared on Thursday that the AstraZeneca vaccine is safe and effective. The EMA said the benefits of the vaccine far outweigh the potential risks — and pointed out that the rate of post-vaccine blood clots was actually lower than the expected rate in the general population.
Now, a group of German researchers, led by professor Andreas Greinacher at the University of Greifswald, said on Friday in a statement that they believe the AstraZeneca vaccine, in some cases, prompts overactivation of platelets in the blood, which can then cause potentially deadly clots. They said it's similar to what happens with a condition called heparin-induced thrombocytopenia.
Greinacher and his colleagues analyzed the 13 cases of cerebral blood clots reported in Germany following the administration of roughly 1.6 million doses of the AstraZeneca vaccine in that country. Of the 13 cases, 12 were women, and all the cases occurred between four and 16 days after the shot was administered. The EMA had also noted that almost all the reported clotting incidents were in women under the age of 55.
Greinacher and his colleagues say that in four of the patients, they were able to isolate and identify the specific antibodies that provoke the immune reaction leading to the cerebral blood clots.
Professor Pål Andre Holme told the Norwegian newspaper VG that he's confident they've identified antibodies prompted by the vaccine that caused an overreaction by the immune system leading to the blood clots.
"Our theory that this is a strong immune response that most likely comes after the vaccine," Holme said. It's the same theory that Greinacher and his colleagues have put forward in Germany.
The findings of a large U.S. trial have shown that the coronavirus vaccine developed by AstraZeneca and the University of Oxford is 79% effective in preventing symptomatic illness and 100% effective against severe disease and hospitalization.
The safety and efficacy analysis of the AstraZeneca vaccine, published Monday, was based on 32,449 participants across 88 trial centers in the U.S., Peru and Chile.
Data from the late-stage human trial study reaffirms that the Oxford-AstraZeneca vaccine is safe and highly effective.
By comparison, Moderna’s vaccine has been found to be more than 94% effective in preventing Covid and Pfizer-BioNTech’s vaccine was found to be 95% effective.
AstraZeneca said it will continue to analyze the data and prepare for the primary analysis to be submitted to the U.S. Food and Drug Administration for emergency use authorization in the coming weeks.
The results come shortly after several countries temporarily suspended the use of the shot following reports of blood clots in some vaccinated people. Health experts sharply criticized the move, citing a lack of data, while analysts expressed concern about the impact on vaccine uptake as the virus continues to spread.
Many European countries suspended use of AstraZeneca’s vaccine earlier this month following initial reports of the symptoms, which have led to at least 15 deaths. Most resumed vaccinations after the European Medicines Agency (EMA) recommended doing so on 18 March, saying the benefits of the vaccine outweigh any risks. EMA is continuing to investigate the matter and will convene a Now, a group of researchers led by German clotting specialist Andreas Greinacher of the University of Greifswald says the highly unusual combination of symptoms—widespread blood clots and a low platelet count, sometimes with bleeding—resembles a rare side effect of the blood thinner heparin, called heparin-induced thrombocytopenia (HIT).
The scientists, who first described their findings during a 19 March press conference, recommend a way to test for and treat the disorder and say this can help ease worries about the vaccine. “We know what to do: how to diagnose it, and how to treat it,” says Greinacher, who calls the syndrome vaccine-induced prothrombotic immune thrombocytopenia, or VIPIT. Greinacher says he has submitted a manuscript to the preprint server Research Square.
Even if Greinacher’s mechanism isn’t the whole story, multiple researchers told Science they were convinced that the vaccine was causing the rare set of symptoms. If that turns out to be true, it could have major consequences for the vaccine, which is one of the cornerstones of the World Health Organization’s push to immunize the world. AstraZeneca is working with partners around the globe to make and distribute billions of doses in low- and middle-income countries, which might have a harder time identifying and treating rare side effects.
Europe is relying heavily on the vaccine as well; the European Union bought 400 million doses. The company's failure to deliver on time has delayed vaccine rollouts on the continent, but now, dented confidence is exacerbating the delays. And even if the risk is very low, it may make sense to use the vaccine only in those who also stand to gain the most from it: elderly people at high risk of dying from COVID-19. Several European countries have started to do this. The situation has scientists walking a tightrope: They want to make the medical profession aware of their concerns without sowing panic.
But Greinacher's hypothesis is being taken seriously. Two German medical societies put out press releases lauding him for solving the issue. In the Netherlands, the Dutch Internal Medicine Society urged internists to be aware of the symptoms and the recommended course of action. The United Kingdom has officially reported only 5 cases—despite administering 11 million doses of the AstraZeneca vaccine—but the British Society of Haematology has urged its members to be aware of “an important and emerging area of haemostasis and thrombosis practice” and to report any possible cases. The Australian Technical Advisory Group on Immunisation has recommended against giving any COVID-19 vaccine to people with a history of HIT.
It is not yet clear how the vaccine could trigger VIPIT, and not everyone thinks the case is closed. “It’s intriguing, but I am not entirely convinced,” says Robert Brodsky, a hematologist at Johns Hopkins University. AstraZeneca, meanwhile, has not directly responded to the reports of the rare constellation of symptoms except to say that they did not appear in any of the company’s clinical trials.
“People are absolutely working like crazy behind the scenes to provide more clarity,” says Saskia Middeldorp, a vascular internist at Radboud University Medical Center in the Netherlands, who disagreed with the temporary halt of the vaccine because she says the benefits clearly outweigh the risks.