As another pandemic wave staggers Europe, the continent’s top drug regulator said on Thursday that the AstraZeneca vaccine was safe, hoping to allay fears of possible side effects from a shot that is a vital weapon in the anti-coronavirus arsenal, and prompt more than a dozen countries to resume using it.
But the regulator, the European Medicines Agency, said a new warning label would be added to the vaccine so that people in the medical community could be on the lookout for a potential rare complication leading to blood clots and bleeding in the brain.
Despite reports of a small number of cases of dangerous blood clots in people who had received the vaccine, a review of millions of cases found that it does not increase the overall risk of clots, though “there are still some uncertainties,” said Dr. Sabine Straus, who heads the agency’s risk assessment committee.
The E.M.A., an arm of the European Union, signaled that even if that threat proves to be real it is a small one, and the AstraZeneca shot, like many other drugs considered effective and safe, will prevent vastly more illness and death than it might cause — the same message conveyed by the World Health Organization and independent experts. Officials want to bolster confidence in a crucial vaccine, and in a stumbling European inoculation campaign that has fueled mistrust of governments across the continent.
The stakes are enormous: Even as it recedes in the United States and elsewhere, the virus is once again on the rise in Europe, killing more than 20,000 people per week, filling hospitals and prolonging the economic suffering from shutdowns. The W.H.O. said on Thursday that Europe was not inoculating people quickly enough to slow transmission, new infections had risen for three straight weeks, and more people in the region were dying from Covid-19 than a year ago.
Trust in the AstraZeneca vaccine is essential to fighting the pandemic worldwide. The shot, more easily stored and less expensive than Pfizer’s or Moderna’s, and sold for now without the goal of earning a profit, is a keystone of the W.H.O.’s effort to inoculate poor and middle-income countries.
Last week and early this week, several European countries suspended use of the AstraZeneca vaccine, a pause that, however brief, threatens lingering consequences both on that continent, which is struggling to contain a new wave of infection, and around the world.
“This is a safe and effective vaccine,” said Emer Cooke, the head of the European regulator.
Within hours, Germany, Italy, France and Spain said they would promptly resume using it, though Norway said it would await further study. A fearful public may not be easily reassured.
“I haven’t decided yet whether I am going to get vaccinated or not,” said Giada Pietrolillo, a kindergarten teacher in Calabria, at the southern tip of Italy. “I am not sure I trust anyone any more.”
While the vast majority of the roughly 20 million people in Europe who have received the AstraZeneca shot suffered no serious side effects, Dr. Straus said, there were a handful of troubling cases of cerebral venous thrombosis, blood clots in the brain that lead to hemorrhages, in patients who also had low platelet counts. The evidence, she said, is not conclusive as to whether it is related to the vaccine.
The officials said they hoped a clear statement on the safety of the vaccine would calm anxious governments and their populations at a particularly precarious moment in the pandemic.
AstraZeneca has said that a review of 17 million people who received the vaccine found they were less likely than others to develop dangerous clots.
Manuela Perozzi, a teacher for handicapped pupils at a middle school in Campobasso, in southern Italy, said she was sick with fever and aches for two days after her first dose of the AstraZeneca shot earlier this month, and then grew worried as fears about it spread.
“We can only try to hold on to science,” she said. “But surely I will be even less serene when they call me for the second shot.”
The leaders of the nations, mostly in Europe, that paused its use earlier this week framed their decision as a move to reassure the public that all concerns were being treated seriously.
Despite their differences, all the vaccines approved by Western regulators have shown themselves to be remarkably effective at reducing severe illness and death. And though the AstraZeneca vaccine accounts for less than 20 percent of the hundreds of millions of doses ordered by the European Union, it was a critical part of early rollout plans.
With infections again on the rise in many European countries, the cost of delay may be measured in lives.
This week, more people are on ventilators in hospitals in Poland than at any time in the pandemic, leading officials to reimpose national restrictions, starting on Saturday. Italy has reimposed lockdowns in the hopes of limiting outbreaks. Across the continent, there is rising concern about the spread of variants of the virus.
Hans Kluge, the W.H.O.’s regional director for Europe, told reporters that the continent recorded more than 1.2 million new cases last week. In Paris, the head of public hospitals in the capital region said that the situation was increasingly dire and that the authorities were struggling to find enough beds in intensive care units.
President Emmanuel Macron of France said on Wednesday: “We are living through the hardest weeks now. We know it.”
The hope had been that, by this time, vaccinations would allow governments to avoid reimposing the often draconian restrictions that have been a part of life across Europe for the past year.
The suspensions of the AstraZeneca vaccine underscored how even relatively minor disruptions could have outsize impact as the global supply remains exceedingly tight.
“Demand outstrips supply to such a large degree right now, even the slightest hiccup is felt keenly,” said Andrea Taylor, assistant director at Duke University’s Global Health Innovation Center. “There is no slack in the system.”
Both vaccine makers and governments, she said, have repeatedly offered optimistic projections that do not factor in hitches in the production process.
“They seem surprised every time a production problem causes a slowdown in delivery, as though that is a wholly unexpected event.” she said. “It shouldn’t be.”
Few countries in the world find themselves in the enviable position of the United States — which has secured more than enough doses for every person in the country. The Biden administration said Thursday that it would send millions of doses of the AstraZeneca vaccine, which has yet to be authorized by the Food and Drug Administration, to Mexico and Canada.
Even Britain, which moved quickly to procure vaccines and has been rapidly administering doses to most people over the age of 50, has been forced to shift its strategy in part to deal with dips in supply.
Starting late last year, British regulators allowed an increased gap between the two doses of vaccine required for maximum protection: up to 12 weeks, rather than the three or four weeks used in clinical trials.
That has allowed Britain to give initial protection to about 25 million people. But many of them will soon need a second dose, putting pressure on the system and leading officials to warn that distribution in April will move slower.
In Europe, where countries have largely stuck to the tighter dosing strategy, the AstraZeneca vaccine was already a focus of controversy, in part as a consequence of confusing initial trial results, communication blunders by the company and delays in supply.
The immediate challenge for leaders across Europe will be to restore faith in the AstraZeneca vaccine.
Concerns about it arose from reports of a small number of recipients who developed blood clots or abnormal bleeding.
The most concerning came from Norway and Germany, involving cases where blockage developed in veins that drain blood from the brain in patients who also had lowered platelets.
After several cases came to the attention of the Paul Ehrlich Institute, the agency in charge of vaccine safety in Germany, the use of the vaccine was halted there and other European countries followed suit.
Klaus Cichutek, the head of the institute, said that it had acted after seven cases of cerebral venous thrombosis had occurred four to 16 days after vaccination.
An analysis by the institute suggested that only a single case would normally be expected among the 1.6 million people who received the vaccine in that time window.
The institute said that it had convened a group of experts on Monday and that they had agreed unanimously that a link to the vaccine was not implausible and should be investigated.
In Norway, a group of researchers from Oslo University Hospital said on Thursday that two deaths and two other cases of severe reactions were probably caused by the vaccine.
“Our theory that this is a powerful immune response which most likely was caused by the vaccine has been found,” said Pål Andre Holme, a chief physician at the hospital. “We have found specific antibodies against blood platelets that can cause these reactions,” he added, which have also been known to result from use of other drugs.
Ms. Cooke said that it was important to closely monitor all side effects.
“We are also launching additional investigations to understand more about these rare cases,” she said. But the regulatory agency found that the benefits of the vaccine — at a moment when thousands are still dying around the world every day — outweighed the risk.
“If it was me,” Ms. Cooke said. “I would be vaccinated tomorrow.”
Reporting was contributed byNick Cumming-Bruce from Geneva, Gaia Pianigiani from Rome and Henrik Pryser Libell from Oslo.