BRUSSELS — First it was AstraZeneca. Now Johnson & Johnson.
Last week, British regulators and the European Union’s medical agency said they had established a possible link between AstraZeneca’s Covid-19 vaccine and very rare, though sometimes fatal, blood clots.
On Tuesday, Johnson & Johnson said it would pause the rollout of its vaccine in Europe and the United States over similar concerns, further compounding the continent’s one-step-forward-two-steps-back efforts to quickly get people immunized against the coronavirus.
European officials had been confident that they had secured enough alternative vaccine doses to take up the slack of the AstraZeneca problems and achieve their goal of fully inoculating 70 percent of the European Union’s adult population — about 255 million people — by the end of the summer. On Tuesday, European officials did not immediately say whether they believed the milestone would also survive the Johnson & Johnson suspension.
They have been pinning their hopes on at least 300 million doses that are expected to arrive in the region this month and in May and June — two-thirds of which are from Pfizer, which has had a good track record of delivering to the European Union.
The troubles with two major vaccines are casting a cloud over the European Union’s vaccine rollout just as it has finally begun to gain momentum after months of short supplies and logistical problems.
There is mounting evidence that the concerns are eroding Europeans’ willingness to get the AstraZeneca vaccine in particular, and threatening to elevate already high levels of vaccine hesitancy generally.
New and seemingly arbitrary guidelines, which vary nation to nation, around the use of the AstraZeneca vaccine have added to the consternation of Europeans who are still waiting to be vaccinated.
The AstraZeneca vaccine is still being given to older people across the bloc. But some countries have restricted its use for younger demographics. Britain has drawn the line at age 30. In France and Belgium it is 55. In Germany, Italy and Spain, 60. Other nations, like Norway and Denmark, are not administering the AstraZeneca vaccine at all.
It has not helped that the new guidance not to give the AstraZeneca shot to younger people is the opposite of what was recommended when it was first introduced in Europe, when many countries gave it only to younger people because early data did not include large numbers of older people in clinical trials.
The confusion is taking its own toll. According to a YouGov poll published last month, 61 percent of the French, 55 percent of Germans and 52 percent of Spaniards consider the AstraZeneca vaccine “unsafe.” That is in stark contrast to the findings of a similar poll from February, when more people in those countries, with the exception of France, believed that the shot was more safe than unsafe.
Regulators have asked vaccine recipients and doctors to be on the lookout for certain symptoms, including severe and persistent headaches and tiny blood spots under the skin. Doctors’ groups have circulated guidance about how to treat the disorder.
In Poland, where the vaccination campaign relies to a large extent on AstraZeneca and where its use has not been restricted, a recent poll showed that given a choice, fewer than 5 percent of Poles would choose the AstraZeneca shot.
Almost everywhere across the European Union, it seems, many are eager for alternatives, as the new types of vaccines that include the Moderna and Pfizer, which utilize science known as “mRNA,” have not been associated with similar side effects.
Data from the 27 E.U. member states by the European Center for Disease Prevention and Control shows that over all, 80 percent of vaccine doses distributed to the bloc have already been administered. That share drops to 65 percent for AstraZeneca, however, suggesting that many of its doses are sitting unused.
Yet it is hard to predict how serious a blow the latest twist in the AstraZeneca saga — and the new Johnson & Johnson concerns — will be to E.U. vaccination efforts, as officials in Brussels have made big if belated efforts to turbocharge the second-quarter supply of doses.
The European Union is poised to receive at least 300 million doses of various vaccines, three times what it got in the first quarter. Two hundred million are slated to come from Pfizer/BioNTech. Moderna is expected to deliver 35 million doses. Another 55 million doses are due of the Johnson & Johnson jab, and 70 million from AstraZeneca.
In the rosiest scenario, the European Union could get up to 360 million doses by June.
On Thursday, after Spain’s government changed the age threshold for the AstraZeneca shot, two-thirds of people called up for vaccination in Madrid did not show up, Antonio Zapatero, the regional health minister, told a news conference on Friday.
He attributed the no-show by 18,200 people to “confusion” generated by Spain’s central government, which said on Wednesday that the AstraZeneca vaccine should be given only to people over 60. Before this change, Mr. Zapatero said, the rate of abstention was 2 percent.
Yves Van Laethem, a top epidemiologist who is the country’s Covid task force spokesman, said he expected a two-week delay that would mostly affect younger age groups in late summer. He said the E.U. regulator guidance had only partly helped in clarifying the situation.
The European Medicines Agency’s opinion “wasn’t very clear, and it is also part of the problem,” Dr. Van Laethem said in an interview. “When you say, ‘We don’t apply limitations, but we just say there are serious side effects,’ there is part science and part diplomacy in that.”
He said the limited effect that the new AstraZeneca issues would have on Belgian’s rollout was in large part because the country had ordered big shares of other vaccines.
Although all E.U. countries have been offered a chunk of each vaccine approved in the bloc so far — AstraZeneca, Johnson & Johnson, Moderna and Pfizer — many opted to forgo parts of their share of more expensive or cumbersome vaccines like Pfizer and Moderna early on, instead favoring the AstraZeneca jab.
“In Britain or Eastern Europe, a big part of the campaigns are based on AstraZeneca,” Dr. Van Laethem said.
Wealthier bloc members like Denmark, France, Germany and the Netherlands can better compensate for the loss of confidence in AstraZeneca, because they acquired extra doses of other vaccines — especially Pfizer — through a secondary market after poorer E.U. nations gave theirs up.
Those countries — including Bulgaria, Croatia, Latvia and Slovakia — are likely to be less able to quickly offer alternatives.
Dr. Van Laethem, the Belgian immunologist, said that the national and European authorities needed to better communicate the costs and benefits of taking the AstraZeneca dose versus and the other authorized vaccines.
Experts worry that even limited concerns over one vaccine’s unlikely side effects can affect people’s overall willingness to be immunized.
“The main thing is to make people understand that the problem is the virus,” he said. “We have to vaccinate people — the risk linked to the virus is higher than those rare side effects,”
Raphael Minder contributed reporting from Madrid and Constant Méheut from Paris.