IE 11 is not supported. For an optimal experience visit our site on another browser.

Oxford-AstraZeneca vaccine delays over blood clot fears raise new doubts over Europe's rollout

"If this was a serious issue it would have come up," said Professor Mukesh Kapila.

LONDON — Several European countries halted the rollout of the world-leading Oxford-AstraZenaca Covid-19 vaccine this week because of reports some patients suffered blood clots.

However, some experts and regulators say, not only were these decisions based on misunderstood evidence, but they also risk increasing anxiety in one of the most vaccine-hesitant parts of the world.

"We need to be ultracautious — but now this is being overly cautious," said Mukesh Kapila, a former adviser to the director-general of the World Health Organization, who has held senior roles at a host of other United Nations agencies.

"We have real-world information from tens of millions of vaccinated patients, and if this was a serious issue it would have come up," added Kapila, now an emeritus professor of global health and humanitarian affairs at Manchester University in the United Kingdom.

German police officer Dirk Moeller registers to get an AstraZeneca vaccination against Covid-19 at the former Tempelhof airport in Berlin on Monday. Tobias Schwarz / AFP - Getty Images

On Thursday, Denmark announced it was pausing its rollout of the vaccine developed by Oxford University and the British-Swedish pharmaceutical giant AstraZeneca. This came after reports of dozens of people having blood clots after receiving the shots, including at least one person who died in the Nordic country.

Norway, Bulgaria and Iceland followed suit, while other countries including Estonia, Lithuania, Luxembourg, Latvia, Italy and Austria halted specific batches that they said might be associated with the illnesses.

These countries stressed that no link had been confirmed and that the move was a temporary measure until they could gather more evidence. Denmark said it was using the "precautionary principle" — the idea that until you have more evidence, it's better to be safe than sorry.

Download the NBC News app for full coverage of the coronavirus outbreak

However, some experts say, this appears to be a classic case of confusing causation with correlation: Just because someone got sick after being vaccinated, it doesn't mean the vaccine caused it, they say.

The European Medicines Agency, the continent's main drug regulator, said that as of Thursday, 30 blood clots have been reported out of 5 million vaccinated patients — about the same number as would be expected in the nonvaccinated population.

Britain, which has vaccinated more than 20 million people, most of them with the AstraZeneca shot, said much the same. Both the European Medicines Agency and the WHO said they will investigate the cases, but emphasized that as far as they are concerned this vaccine is safe and effective.

AstraZeneca said in an emailed statement that its own data of more than 10 million patient records showed the incidence of blood clots was actually lower than the general population's rate.

Europe is the most vaccine-hesitant continent in the world, according to a survey by the British charity The Wellcome Trust. In particular, AstraZeneca has taken a public relations battering after several European regulators and leaders, including French President Emmanuel Macron, suggested there wasn't enough data to prove its effectiveness in people over the age of 65.

Real-world evidence suggests that is not true, but the damage to public trust was already done. At one point last month, there were millions of AstraZeneca vaccines sitting unused in storage in countries such as Germany and France, partly because people were reluctant to take them, according to officials.

German Health Minister Jens Spahn said Friday he did "regret" seeing neighboring Denmark suspend the shots despite what he described as a lack of evidence.

The United States has pledged some $1.2 billion toward the development of the AstraZeneca vaccine and ordered 300 million doses. But it is yet to be approved in the U.S. amid questions over the transparency of the initial phase 3 trial data and a delay to the study being conducted in the U.S.

At the heart of this debate is the delicate balance that needs to be struck by public health officials and governments: vigilance against any possible side effects, transparency to maintain public trust, but also not giving credence to shaky claims that might unduly damage faith in these vaccines.

"It's a bit of a tricky issue because there is also a danger in playing down these concerns," according to Hajo Zeeb, a professor at Germany's Leibniz Institute for Prevention Research and Epidemiology. "Do you say that you're staying on the side of caution, or do you say, 'No we are not seeing anything out of the ordinary,' and carry on vaccinating like we are in Germany?"

A healthcare worker with a syringe filled with the AstraZeneca vaccine during a vaccination rollout for teachers in Ronda, Spain, last month. Jon Nazca / Reuters file

One such debate arose in the United Kingdom in 2009 after a 14-year-old high schooler died hours after receiving a vaccination for human papillomavirus, also known as HPV, which can cause cancer.

David Salisbury, the British government's director of immunization at the time, said they decided to withdraw that batch of vaccine but they never stopped the vaccination campaign.

Crucially, he said, his team refused to make any comments to the media until the cause of death was known, which turned out the next day to be a malignant tumor and unrelated to the shot.

"The story fell off the news pretty quickly thereafter," Salisbury told NBC News on Friday. Now, he fears that halting the AstraZeneca shot based on hazy evidence means "the story will spread, and of course it won't help" overcome vaccine hesitancy.