This story will be updated.
BERLIN — Experts at Europe’s medical regulator were meeting Thursday to determine whether AstraZeneca’s coronavirus vaccine may be linked to rare blood clots seen in a small number of patients who received the shot.
The suspensions have split both the scientific community and the countries in Europe, with some continuing their vaccination campaigns as others warn that the extremely unusual and deadly nature of blood clots detected, even if in small numbers, warrant caution.
Even if the European regulator says there is no link between the vaccine and blood clots, experts say the damage has been done, with trust in the vaccine already diminished. The pause comes as several European countries warn they are at the beginning of a third wave of the pandemic, with an already slow pace of vaccinations and new more contagious variants spreading rapidly.
The potential ramifications stretch much further than the continent. Easier to store and handle than other products on the market, the offering from AstraZeneca, which developers have said will be distributed on a not-for-profit basis, is a major tool in the fight against the spread of the coronavirus in developing countries.
AstraZeneca has said that the 37 blood clotting incidents reported among the 17 million shots given in Europe are far lower than to be expected in the normal population, and the World Health Organization has said it continues to think that the benefits outweigh the risks.
Experts from the EMA agreed on both counts, but said their investigation was focused on a small number of normally extremely rare brain clots that have been reported in countries, including Germany and Norway, following vaccinations, including in younger people and notably among women.
“The primary assessment is a vigorous scientific assessment, looking at all the available evidence, to see whether the evidence would suggest a causal link between these very rare but serious events that we’ve seen and vaccination, or whether they are coincidental,” Peter Arlett, the head of safety monitoring for the EMA, said in a news conference Tuesday.
If it is decided there is a causal link to the vaccine, then there will be a “very careful consideration” of whether something put those patients at particular risk, he said.
In Britain, where 11 million shots have been administered, almost double the amount across the entire European Union, the medical regulator continues to urge people to get their vaccines.
June Raine, the chief executive of the Medicines and Healthcare Products Regulatory Agency, Britain’s counterpart to the EMA, said they had received a “very small number” of reports of “an extremely rare form of blood clot” in the brain along with lower levels of platelets following vaccination, but that such events could occur among those who haven’t been vaccinated, or those who have coronavirus.
“While we continue to investigate these cases, as a precautionary measure we would advise anyone with a headache that lasts for more than 4 days after vaccination, or bruising beyond the site of vaccination after a few days, to seek medical attention,” she said in a statement on Thursday.
Concerns were first triggered in Austria in early March. As the country vaccinated medical workers, a 46-year-old nurse died of multiple blood clots. Another medical worker at the same hospital suffered a pulmonary embolism. Austria suspended use of that batch as a precaution.
Last week, Europe’s regulator said that it found no evidence of a causal link with the vaccine in those cases.
Given that decision, Germany had initially said it would go ahead with its AstraZeneca vaccinations, with its health minister assuring people of its safety on Friday. But it reversed course after recording three new cases over the weekend of unusual blood clots in the brain among those vaccinated, adding to four other cases. It has since reported one more case. Three people have died.
Germany said that among the 1.6 million doses of the vaccine administered, the eight cases of a rare type of blood clot, called cerebral venous sinus thrombosis, which occurs in a vein in the brain is higher than one would normally expect.
It said that among a group that size, one case could normally be expected. Oral contraceptive pills are also considered a risk factor for the rare kind of stroke, which Johns Hopkins University says normally affects about 5 people in 1 million each year.
Given the seriousness of the condition, Germany said it had little choice but to pause until there was an expert review.
Steinar Madsen, medical director at the Norwegian Medicines Agency, said all four people were under 50 years old, and that two are now dead.
He described the type of blood clot as very rare. “What I can say is that this picture with low platelet counts, blood clots and internal bleeding is very unusual,” he said. “Even experts have not seen cases directly similar to this.”
Experts at Oslo University Hospital said Thursday they think there is a link to the vaccine and three cases of hospitalizations there.
“Our findings support the early theory that the patients had a strong immune response, which led to antibody creation which can ignite blood platelets and cause a thrombosis,” said Pål Andre Holme, the lead physician looking into the cases. He said he could not be certain that the vaccine was the cause, but “I see no other possibility as of today.”
He said he was “surprised” by his team’s findings and that he had not seen a similar response caused by other vaccines. He said his team is continuing its studies and cannot yet say whether the three health workers shared any underlying conditions that could explain why they had such a reaction to the vaccine.
Denmark has recorded one death in a 60-year-old recently vaccinated woman, who had “a highly unusual disease pattern,” which also included a low platelet count and blood clots in small and large vessels.
Spain has said it has had one such case in a 46-year-old teacher who died of a blood clot to the brain, which contributed to its decision to pause its rollout.
But there has been fierce pushback from some parts of the scientific community, particularly in Britain.
Ian Douglas, a professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said there appears to be no strong evidence that the events are causally related, though he didn’t rule it out.
He said that even if the vaccine was causing some concerning side effects, those most be weighed in a risk-benefit analysis: How serious are the side effects and how numerous when balanced against the drug’s benefits.
“We do this all the time with all medicines,” he said. “You have to weigh the risks and benefits.”
Douglas said he was deeply concerned that the actions taken by European countries would reduce use of this or any vaccine and that European countries acted rashly. To pause the AstraZeneca vaccine, which is desperately needed, requires a higher level of certainty of harmful effects than has been shown, he said.
“If you take action too early it is very easy to lose trust,” he said. “Confidence is easily lost and less easily regained.”
Experts in Germany have speculated that Britain may not be picking up as many similar cases because it began with vaccinations of older people, generally at lower risk of such complications and a population in which deaths might be less notable.
Klaus Cichutek, president of the Paul-Ehrlich-Instituts, Germany’s regulator, said they had analyzed “large data sets” from Britain and found few cases.
“But the focus and the gaze was not yet focused on such cases either,” he told German broadcaster ARD. “On the other hand, it may be the case that in the U.K. another age group, another population group, was vaccinated.”
Some have alleged that the decision in some countries to suspend the vaccine is political. Paul Hunter, a professor of medicine and infectious diseases at the University of East Anglia, said evidence of a link was weak and he believed herd mentality was at play.
“If Germany is doing this, we don’t want to be seen as less protective than the Germans,” he said. “Many people, including me, don’t think this is real. This is very likely a random association — and not a causal relationship.”
Hans Kluge, the World Health Organization’s Europe director, reiterated Thursday that blood clots occur all the time. The detection and reporting of such events is testament to strong surveillance systems, he said.
“In vaccination campaigns, it is routine to signal potential adverse events,” he said. “This does not necessarily mean that the events are linked to the vaccination.” The WHO is conducting its own assessment and has said details will be made public as soon as possible.
Even before the concerns over blood clots, AstraZeneca had been suffering from an image problem in Europe. Trial data came under fire from the scientific community, while there was also confusion over dosing and efficacy rates.
In Europe there had been reports that AstraZeneca appointments were not being taken up amid particular skepticism over its efficacy.
“Even if it turns out that the vaccine is harmless for most, it will unfortunately not be easy to rebuild trust,” Ulrich Weigeldt, chairman of the German Association of General Practitioners, told Redaktionsnetzwerk Deutschland on Thursday.
Martin Selsoe Sorensen in Copenhagen contributed to this report.
