A cascading number of European countries - including Germany, France, Italy and Spain - have suspended use of AstraZeneca's COVID-19 vaccine over reports of dangerous blood clots in some recipients, though the company and international regulators say there is no evidence the shot is to blame.
AstraZeneca's formula is one of three vaccines in use on the continent. But the escalating concern is another setback for the European Union's vaccination drive, which has been plagued by shortages and other hurdles and is lagging well behind the campaigns in Britain and the US.
The EU's drug regulatory agency called a meeting for Thursday to review experts' findings on the AstraZeneca shot and decide whether action needs to be taken.
The furor comes as much of Europe is tightening restrictions on schools and businesses amid surging cases of COVID-19.
Germany's health minister said the decision to suspend AstraZeneca shots was taken on the advice of the country's vaccine regulator, the Paul Ehrlich Institute, which called for further investigation into seven cases of clots in the brains of people who had been vaccinated.
"Today's decision is a purely precautionary measure," Jens Spahn said on Monday.
French President Emmanuel Macron said his country would likewise stop dispensing the vaccine until at least Tuesday afternoon. Italy also announced a temporary ban, as did Spain, Portugal and Slovenia.
Other countries that have done so in the past few days include Denmark, which was the first, as well as Ireland, Thailand, the Netherlands, Norway, Iceland, Congo and Bulgaria. Canada and Britain are standing by the vaccine for now.
Venezuela's Vice-President Delcy Rodriguez on Monday said the government would not authorise the vaccine, citing unspecified "effects on patients".
In the coming weeks, AstraZeneca is expected to apply for US authorisation of its vaccine. The US now relies on Pfizer's, Moderna's and Johnson & Johnson's shots.
AstraZeneca said there have been 37 reports of blood clots out of more than 17 million people vaccinated in the 27-country EU and Britain. The drug maker said there is no evidence the vaccine carries an increased risk of clots.
In fact, it said the incidence of clots is much lower than would be expected to occur naturally in a general population of this size and is similar to that of other licensed COVID-19 vaccines.
The World Health Organisation and the EU's European Medicines Agency have also said the data does not suggest the vaccine caused the clots and people should continue to be immunised.
"Many thousands of people develop blood clots annually in the EU for different reasons," the European Medicines Agency said. The incidence in vaccinated people "seems not to be higher than that seen in the general population".
The agency said that while the investigation was going on, "the benefits of the AstraZeneca vaccine in preventing COVID-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects".
Blood clots can travel through the body and cause heart attacks, strokes and deadly blockages in the lungs. AstraZeneca reported 15 cases of deep vein thrombosis, or a type of clot that often develops in the legs, and 22 instances of pulmonary embolisms, or clots in the lungs.
The AstraZeneca shot has become a key tool in European countries' efforts to boost their sluggish vaccine rollouts. It is also pillar of a UN-backed project known as COVAX that aims to supply COVID-19 vaccines to poorer countries. That program continues unaffected by the European suspension.
Pfizer's and Moderna's vaccines are also used in Europe, and J&J's one-shot vaccine has been authorised but not yet delivered.
Dr Michael Head, a senior research fellow in global health at the University of Southampton in England, said there was no data yet to justify suspending the AstraZeneca vaccine and called the decision "baffling".
"Halting a vaccine rollout during a pandemic has consequences," Head said. "This results in delays in protecting people, and the potential for increased vaccine hesitancy, as a result of people who have seen the headlines and understandably become concerned."
Australian Associated Press