Use of the Oxford/AstraZeneca vaccine was halted across much of Europe today, including in France, Germany, Italy and Spain.

Why it matters: The suspensions followed reports that a small number of patients who received the vaccine experienced blood clots. But public health agencies, including the World Health Organization and the EU’s own medical arm, say there’s no indication that the blood clots were caused by the vaccine, or that the risks of giving the shot outweigh those of delaying it.

• AstraZeneca says that out of the 17 million people who have received the vaccine in the EU and U.K., the number experiencing such symptoms is actually lower than would be expected in the general population.
• Still, safety boards from the WHO and the European Medicines Agency (EMA) will convene on Tuesday to discuss the situation.
• The state of play: The vaccine has been approved by the WHO and some 70 countries. Real-world data from the U.K., where the vaccine has been used most widely, suggests it's highly effective at preventing serious cases. No blood clotting concerns have been reported there.

Driving the news: Denmark and Norway were first to suspend the shot last Thursday, and the EU’s most populous countries followed suit today, with leaders describing the suspensions as precautionary.

• French President Emmanuel Macron said distribution would be halted for 24 hours pending an EMA assessment.
• Some experts fear such moves risk increasing vaccine hesitancy and further slowing distribution at a dangerous time, given the ongoing vaccine shortages and fast-spreading variants.
• Indonesia cited the situation in Europe today in delaying its rollout, while Canadian Prime Minister Justin Trudeau reassured Canadians that the vaccine was safe, and leaders in the U.K. defended the homegrown jab.

The big picture: This is arguably the most important vaccine in the world in the near term. Around 3 billion doses have been reserved to date, and more than half are destined for developing countries.

• The vaccine is relatively affordable (it’s not being sold for a profit) and easy to transport and store compared to the Pfizer and Moderna shots.
• The COVAX initiative is sending AstraZeneca doses all over the world, often to countries that have no other source of vaccines.

Yes, but: The rollout of the vaccine in Europe has been plagued by confusion, distrust and even animosity.

• AstraZeneca has delivered only half the doses it promised the EU, leading to anger and in one case an export ban.
• The doses that have arrived have been administered remarkably slowly due to hesitancy among the public — fueled in part by skeptical rhetoric from politicians like Macron — and delays in granting approval for people over 65.

In the U.S., which ordered 300 million doses, the vaccine has still yet to be approved.

• AstraZeneca’s U.S. trial was paused for seven weeks last fall. Concerns about the company's trials intensified after it emerged that some British participants had been mistakenly given a half-strength dose (surprisingly, they had better results).
• The trial data is now at last being reviewed by independent monitors, and emergency authorization could come in about a month, National Institutes of Health Director Francis Collins told Reuters today.
• Collins said he wasn’t concerned about the reports of blood clots, adding, “There may be a bit of an overreaction to something that is unrelated to the vaccine itself.”

For now, tens of millions of doses are sitting at a facility in Ohio, the NY Times reports.

• The White House has rejected requests to send them abroad — including, reportedly, from the European Union.

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