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.
The European Medicines Agency stressed that the benefits of vaccination still outweigh the risks, as thousands of people die of coronavirus across the continent each day. But British officials advised that adults under 30 be offered alternative vaccines, noting that the calculus is different for young and otherwise healthy people who are at relatively low risk of serious covid-19.
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 European pauses of AstraZeneca inoculations 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," acknowledged Jonathan Van-Tam, England's deputy chief medical officer, 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.
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." Cheap 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 roughly 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 grave side effect.
AstraZeneca said Wednesday that it has been working with the 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 of complications as a result of blood clots after her vaccination in Austria in mid-February. Other cases followed across Europe, with the regulator now putting the risk level at around 1 in 100,000 shots.
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 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 European Medicines Agency's assessment committee, said Wednesday.
A total of 169 cases of CVST have been reported among 34 million people given AstraZeneca across Europe as of April 4, the European Medicines Agency said. In addition there have been 52 other cases of rare blood clots.
It said that it based its scientific review on an initial 62 cases and 18 deaths up until March 22, but continued reports did not change their assessment.
Britain's watchdog said the link to the vaccine was not firmly and officials said they were making new recommendations out of an "overabundance of caution."
As of the end of March, more than 20 million people in Britain had received at least one dose of AstraZeneca, it said. Of those, a review has found 79 people suffered rare blood clots after one dose of vaccine: 51 women and 28 men. Nineteen of those people died. And three of those 19 were under 30 years of age.