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AstraZeneca’s Covid-19 vaccine is facing a crisis of confidence, with one European country after another, as if seized by a fit of panic, temporarily suspending its use over concerns about reports of blood clots in people who received it.

Denmark, Iceland, and Norway had earlier said they would temporarily stop using the two-dose vaccine. On Sunday, Ireland announced a similar decision. France, Germany, and Italy followed on Monday.


Experts and Europe’s regulatory body insist that the vaccine’s benefit — preventing Covid-19 and helping to stop the pandemic — outweighs its risks. They note that the number of people to report the side effect is relatively small, and no causal link has been established.

But experts are also now worried that the decisions by multiple countries to suspend the vaccine’s use could make it harder to convince people to receive it should the concerns turn out, as they expect, to be a false alarm.

“When there are choices, I think the inclination would be that you aren’t stuck, so to speak, with a vaccine if you have questions,” said Sue Desmond-Hellmann, the former CEO of the Bill & Melinda Gates Foundation and a Pfizer board member. She said the concerns may be overstated, and that she is surprised how quickly European countries decided to act.


The decisions, even if temporary, are likely to have other ripple effects.  They put extraordinary pressure on a large clinical trial of the AstraZeneca vaccine being conducted in the United States, which has not authorized the vaccine’s use. And they raise questions about the rollout of a product that, globally, was expected to be produced most inexpensively and distributed most broadly.

In the wake of the decisions by more countries to suspend the vaccine’s use, the European Medicines Agency called an “extraordinary meeting” on Thursday to analyze the risks of the vaccine.

“While its investigation is ongoing, EMA currently remains of the view that the benefits of the AstraZeneca vaccine in preventing COVID-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects,” the agency said in a statement.

The EMA said that the concern is related to blood clots with “unusual features” including low levels of platelets, which are involved in creating clots. Still both the EMA and AstraZeneca emphasized that the number of blood clot-related events, which could include clots in the legs and also more severe outcomes like heart attacks or strokes, seem not to be higher than the rate seen in the general population.

Sir Richard Peto, an emeritus professor of statistics at the University of Oxford, said that there was no good evidence of a hazard, and that he worried that the Norwegian medical agency, which first raised concerns, is not taking into account the underlying risk of clots. Even if vaccine decreased the risk of blood clots in older people, Peto points out, some blood clots would be expected to occur.

“Unless they’ve got serious evidence of hazard, they shouldn’t put out press statements that will very clearly be taken as evidence of hazard,” Peto said.

Side effect scares are common with vaccines, but they also very often do not pan out. The reason is that so many people receive vaccines that some will experience what seems like a side effect by chance when, really, it is not related to the vaccine at all.

“Vaccines protect against one thing: the infection or the infection plus disease,” said Susan Ellenberg, a biostatistician at the University of Pennsylvania who once tracked vaccine side effects at the FDA. “They don’t protect you against everything else that might possibly happen to you.”

That means that right after the vaccine is given to people, some will come down with cancer, or have heart attacks, or suffer falls. “There’s no reason to think that somehow there’s a magical period of time like, you know, four days or a week or two weeks after you get vaccinated, when none of those other horrible things are going to happen to you,” Ellenberg said. 

But for some people, and even for some doctors and health ministers, seeing a strange health occurence happen right after a vaccine is given can make it hard to believe that the vaccine did not cause the problem.

“That’s something that’s very hard for people to process,” Ellenberg said. “That temporal association just gets them every time.”

The risk, she said, is losing an effective and safe vaccine that could help stop the pandemic to a coincidence. It’s happened before, she notes. 

She points to the story of the first vaccine for Lyme disease, developed by SmithKline Beecham in the late 1990s. The clinical trials for the vaccine showed that arthritis occurred at similar rates in both the vaccine and placebo groups. But media reports and suits by plaintiff’s lawyers led to fears among members of the public. Even after a panel of outside advisers to the FDA voted that the vaccine’s benefits outweighed its risks, sales fell so low that the company withdrew the vaccine from the market.

But part of what is feeding the actions taken by individual countries may be that there is less confidence about the AstraZeneca vaccine than for vaccines developed by other companies that are quickly becoming available.

Approvals for the AstraZeneca vaccine are based on clinical trials that were conducted in the U.K., Brazil, and South Africa. Published analyses of the data pool these clinical trials, an unusual strategy. The trial also included information on a second dosing strategy, which used a lower first dose and waited longer between the two doses.

The EMA’s report on the results says “the dossier suffers from a lack of sponsor oversight which impacts the reporting of data and therefore data integrity.” However, it concludes that “the data are sufficiently robust to allow conclusions regarding efficacy and safety.” The EMA estimated the vaccine was about 60% effective, and the data presented show no signs that patients receiving the vaccine were any more likely to develop blood clots than those on placebo.

AstraZeneca has not filed with the U.S. Food and Drug Administration, which likely means the FDA wants to wait for U.S. results, which could come any day.

Desmond-Hellmann, who ran drug development at Genentech, said she believes concerns about AstraZeneca’s vaccine stem at least in part from its rollout.  

She described as “unfortunate” “how it was carried out and how it was communicated. The clinical trial for the AstraZeneca vaccine was extremely confusing and led to, I think, an overall lack of confidence.” 

The AstraZeneca studies, she said, seemed to include “experimental tinkering.” And normally, in a late-stage study, the goal is to have no tinkering at all, but show a clear, definitive result. She emphasized that having many active and safe vaccines is good for the world.

The U.S. study, started last September and including 30,000 patients, is, like the studies for the Moderna and Johnson & Johnson vaccines, being run with the U.S. National Institutes of Health. It’s the best hope for settling any questions or concerns about the AstraZeneca vaccine once and for all.

  • Thank you for your article. As a Notwegian reader it interesting to see how the vaccine halt is perceived in other countries. However I would like to point to that your sources don’t seem to know or represent correctly the reasoning of the Norwegian Health authorities. The reason for alarm is not 4 cases of blood clots out of 120 000 vaccinated. But that the specific constellation of symptoms presented in before this completely healthy people under the age of fifty is a kind of case unknown to the professors treating them at Norways top hospital. So the base rate here is essentially zero, which makes even 4 in 120 000 a worrying find. Another important factor here is that all these 120 000 are under 65 and most of them are Health profesjonals, because Astra zeneca doesn’t have recommendation for at risk groups in Norway. Why do the cases show up in Norway? And not Britain? The frequency of this possible side effect is so low that it will be drowned by the Numbers of the more common blood clots. So you would need the not overwhelmed health system of e.g. Norway, that never have been really overwhelmed by a surge of covid patients to actually discover these «needles in the hay stack». Although rare it does not mean that it would be s good «trade off» to ignore it. Over 12 months with covid Norway ha seen 10 deaths of persons under the age of 50 dead from covid. In one month with astra zeneca we might have 2 deaths of people under the age of fifty. And these two were both completely healthy Health workers. Here is a source (in Norwegian )

  • I agree that tinkering with Phase 3 study designs and doses led to confusion and a perception of lowered credibility. I believe this came from the Oxford side where tinkering is what they do best and do not have experience with developing therapeutics and vaccines.

  • I’m in the U.S. trial. Took both doses in January. No issues. This hysteria about blood clots is unfounded. 2 million doses of the vaccine have been given worldwide. No issues. The number of cases of blood clots is below what normally is expected in the populations. This DNA snippet of the spike protein on the virus is the safest type of vaccine and more stable than mRNA code for making the spike protein. It’s more fragile. That’s why freezers are needed while the J&J and AstraZeneca can be stored at normal refrigeration temps. As a biologist and former health officer, I chose the DNA based vaccine ! I believe these are safer.

    • That is great to hear. I have no concerns regarding the AstraZeneca vaccine, at least no more than taking Pfizer or Moderna. I too am stateside and have yet to be included in a category that can be vaccinated. My preference would be AstraZeneca if it is available in the US by then.

      If you don’t mind GM, from your professional skills and personal experience, why would you choose a DNA vaccine over mRNA?

    • Except Penny that for the Pfizer vaccine there were 22 cases out of 33,000 reports and almost 11 million doses administered. It is a sad fact that EU senior politicians, such as Macron and Merkel have engaged in a series of judgments and assessments that have sought to diminish the AZ vaccine; whereas the evidence from the UK rollout is that it is slightly better, though the difference is statistically insignificant, that the Pfizer vaccine. For instance, Macron said the AZ vaccine was “quasi-ineffective” then the Germans said it should not be given to the over-65’s, shortly followed by the French. Except, again, the evidence from the millions of doses given to people in the UK is that it is very effective in the even the over 80’s. Yesterday the German health minister said “This is a professional decision”, it was “not political”. Yeah, right! Essentially, the EU have been hostile to the UK since BREXIT and the UK decision not to join the EU rollout of vaccines has turned out to be the best bit of judgement since Sir Hugh Dowding told Winston Churchill to stop sending Spirfires to France and keep them in England to fight the Battle of Britain.

  • ‘What is more, one of the most common consequences of serious Covid illness is blood clots.’ Err hello? Isnt that what a vaccine does – mimicks the disease it eventually prevents?

  • What do you mean by “always”?
    Always, since you studied medicine/biochemistry/genetics/whatever,
    and have found convincing research indicating towards dangerous late reactions?
    Or always, since anti-vaxxers spread fear about (real? rare?) long term effects?
    The trouble about “individual comfort” is that we are NOT alone in this, but need to work together. If we want society to protect our rights, life, health – presumably we also need to do our share towards society. Especially, when a virus is not respecting of individual preferences.
    I still don’t get how many Astra doses were administered in relation to how many blood clots, but considering people take backyard manufactured party drugs, head ache pills on alcohol, and happily drive while tired, drunk, or on the phone, I wonder if the Astra risk is really all that high.
    Individually speaking, I’m not keen on brain damage after a covid infection, either.
    But maybe I am so sick of people confusing rational assessment with “preaching”, that I’d be willing to take a terrible risk just to be a living, walking annoyance to anti-vaxxers, should I happen to survive the shot.

    In case this comment be used against me after the Great-Astra-Scandal of ’21 has rendered hundreds or thousands of us dangerously ill: I, too, want safe vaccines. Should there be a true concern, and a disproportionally higher risk with the Astra vaccine, it is good to be wary and have the thing stopped, scrapped, and replaced with better and safer products. Currently though, I find one needs to be sceptic of the sceptics, too.

  • My concern has always been with the unknown long term side effects, particularly with the mRNA vaccines. Short term…Yes, people are different and there is always a risk taking ANY drug or vaccine. When one considers how many times every day the public views advertisements from attorneys regarding pharmaceuticals that went through the full process and received approval that are now the topic of massive lawsuits…..Is it any surprise that many of us are skeptical of something that was created in record time, using a new delivery / vaccination method, and that received EUA leaving the public with no legal recourse if it goes badly? I will wait for a more “normal” approach…Perhas the J&J vaccine…Or perhaps play odds and not vaccinate at all. Everyone will have their own take on this topic. There is no right or wrong in my eyes. Only what the individual is comfortable with. Someone preaching at me about how safe it is will change nothing.

    • Paul – I understand your point of view. However, if we dont get enough people vaccinated…..we dont reach heard immunity. That means more variants are born. God forbid if a new variant comes along that kills off the whole planet.

      I would ask how you would feel about it….but neither of us will be around at that point to discuss how badly you screwed us all. But u do u!!

    • Its not wholly accurate to say that these vaccines were developed in record time…we have been studying mRNA vaccines for 30 years, there was just never the political will and financial support to take them over the finish line until now. So yes, once the vector was identified, a vaccine was on the market in a remarkably short time…warp speed, if you will…but the science has been largely understood for decades. That is really the only reason why we are able to get shots in arms right now. If it was like you said, and we just sort of came up with it within a few months and happened to guess right, then there is no way we would be where we are today.

    • Wouldn’t the long term side effects (if any) be equally likely to be positive as negative? For example, perhaps the vaccines may reduce the risk viral myocarditis or prevent the inflammatory arthridities or stabilize coronary plaque. Unlikely, but then, who knows?

    • Paul and Mike – I too am wary of the mRNA types and even though they have known of this technology for years as someone mentioned, this has NEVER been used on humans until now. I am studying the viral vector types and like the sound of J&J and will be following the AZ conversations of clotting.

  • Why do you not report on how many recipients of the Pfizer BionTech vaccine have experienced blot clots?
    Also, some people say that the Drop in deaths in older people in the UK is ‘ot clearly linked to being vaccinated, often with the AstraZ vaccine. Surely a simple comparison can be made between the blood clot frequency of vaccinated people and not vaccinated ones since all the lockdowns etc. have been going on?

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