BERLIN — Medical regulators in Britain and the European Union on Wednesday said it was "plausible" that the Oxford-AstraZeneca's coronavirus vaccine is linked to rare but sometimes deadly blood clots, a development that could complicate plans to roll it out around the world.
Italy and Belgium also put new restrictions on the vaccine for people under 60 and 55 respectively, bringing them in line with other European countries, including Germany and France.
But the new guidelines marked a particularly notable shift for the United Kingdom, where the government has wholeheartedly backed its homegrown vaccine even as other European countries raised concerns. British newspapers had pounced on initial pauses of AstraZeneca inoculations in Europe as being more about politics than safety, while members of the scientific community had said they were baffled at the decisions.
“This is a course correction,” Jonathan Van-Tam, England’s deputy chief medical officer, said in a televised briefing on Wednesday.
He compared Britain’s fast-moving and relatively successful vaccine campaign to an ocean liner. “If you sail a massive liner across the Atlantic, then it’s not really reasonable that you aren’t going to have to make at least one course correction in that voyage,” Van-Tam said. He called the chances of anyone — including the young — getting unusual blood clots in relation to the AstraZeneca vaccine “vanishingly small.”
Still, the suggestion of a link could have global implications, even as the World Health Organization continues to recommend the vaccine.
AstraZeneca has billed its shot as “a vaccine for the world.” Cheaper and easier to store than others on the market, there are plans to roll it out in more than 140 countries through Covax, a program designed to ensure equitable distribution. But about half the global population is under 30, according to United Nations figures, and many low-income countries have limited ability to diagnose and treat the complicated and potentially serious side effect.
Wednesday’s duel reports also raise questions about how U.S. regulators will handle an application from the company for emergency authorization, especially given that the United States has a comfortable supply of other vaccines.
AstraZeneca said Wednesday it has been working with European regulators to update product information and better understand the individual cases of concern.
“Overall, both of these reviews reaffirmed the vaccine offers a high level of protection against all severities of COVID-19 and that these benefits continue to far outweigh the risks,” it said, adding that the regulatory investigations had been unable to identify any specific risk factors, such as age or sex.
The vaccine has been under intense scientific scrutiny since a 49-year-old nurse died following her vaccination in Austria in mid-February.
Concerns center on a rare condition called cerebral venous sinus thrombosis, or CVST, a clot that stops blood from draining from the brain, which has occurred among those vaccinated at a rate above that normally expected in the population.
“Our conclusion is that these clotting disorders are very rare side effects of the vaccine,” Sabine Straus, chair of the EMA’s assessment committee, said Wednesday.
A total of 169 cases of CVST have been reported among 34 million people given the AstraZeneca vaccine across continental Europe and Britain as of April 4, the EMA said. In addition, there have been 53 other cases of rare blood clots. Although incident rates have differed from country to country, the regulator said that could reflect different reporting standards and estimated the overall risk to be about 1 in every 100,000 shots, in line with rates seen in Germany.
Both E.U. and British regulators said that although the majority of the blood clots have been recorded in younger women, that may reflect who has been getting the vaccine.
Asked whether the risks of the vaccine for young women might outweigh the benefits, EMA’s Straus said, “At the moment, that is something that is very difficult to answer.”
The oral contraceptive pill, which comes with its own risk of blood clots, does not appear to be a risk factor, the EMA said.
British officials said that although 51 of the 79 cases they assessed involved women, looking at the numbers as a proportion of people inoculated with AstraZeneca, there was no difference between women and men.
But Van-Tam said that although the absolute risk might not be higher for younger people, for otherwise healthy people in their 20s, the risk of serious harm from the vaccine slightly outweighed the potential for it to keep them out of coronavirus intensive care wards.
Of the more than 20 million people in Britain who had received at least one dose of the AstraZeneca vaccine as of the end of March, 19 people died of rare blood clots and three of those people were under 30 years of age, officials said.
The EMA said that it is “plausible” that the vaccine is triggering an overactive immune response, which is causing clots medically most similar to those seen in a rare adverse reaction to another drug. Teams in both Norway and Germany have put forward that theory, saying that the antibodies can be detected in lab tests.
The regulators said that AstraZeneca has been asked to conduct more laboratory tests and to provide data from closed clinical trials in an attempt to get a better idea of risk factors.
Peter Arlett, head of pharmacovigilance at the EMA, said J&J’s vaccine “uses a similar technology,” but there have been just three cases of blood clots accompanied by low platelet counts among 4.5 million recipients of that vaccine that “have some similarities” to those seen following AstraZeneca.
Regulators emphasized that for most people — especially the elderly — it is far better to get any safe and effective vaccine than not.
“This vaccine has proven to be highly effective in preventing severe disease and hospitalization, and it is saving lives,” EMA chief Emer Cooke said of AstraZeneca. “Vaccination is extremely important in helping us in the fight against covid-19, and we need to use the vaccines.”
Booth reported from London. Rick Noack in Berlin contributed to this report.