“Our conclusion is that these clotting disorders are very rare side effects of the vaccine,” said Sabine Straus, chair of the EMA’s assessment committee. She said that conclusion was based on incident rates and scientific study, as the organization said that an immune response following vaccination is the “probable” cause of the clots.
So far, most of the cases reported have occurred in women under 60, the regulator said, but it said it still has been unable to work out if particular groups were more at risk than others.
But as the officials spoke, Britain became the latest European country to adjust its vaccination guidelines, saying that adults under 30 should be offered an alternative to the homegrown vaccine developed in cooperation with Oxford University.
AstraZeneca did not immediately respond to a request for comment on Wednesday, but has said that safety remains its highest priority and that it is analyzing its databases of tens of millions of patients to better understand whether there is a higher rate of the clots than otherwise might be expected.
The vaccine has been under intense scientific scrutiny since early last month, when a 49-year-old nurse died of complications due to blood clots following her vaccination in Austria. Other cases followed across Europe, leading some countries to suspend their use of the vaccine until scientific reviews were done.
Concerns center on a rare condition called cerebral venous sinus thrombosis, or CVST, a clot that stops blood from draining from the brain. Regulators have said it is occurring among those vaccinated at a rate above what they’d expect to see in the normal population.
A total of 169 cases of CVST have been reported among 34 million people given AstraZeneca across Europe as of April 4, the EMA 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.
Wednesday’s announcement is the latest blow for the vaccine that was touted as a key tool in leading the world out of the pandemic. Cheap and easier to store than others on the market, there are plans to roll it out in more than 140 countries through a program designed to ensure equitable distribution.
Scientists are still trying to work out if particular parts of the population have an elevated risk. Britain has documented the serious clots in about 1 in 500,000 shots. But higher rates in countries that began using AstraZeneca’s vaccine only among younger people have spurred debate as to whether the risks might be higher for certain age groups or for women. The EMA has estimated the risk to those under 60 to be about 1 in 100,000. It said that the majority of the blood clots have occurred in women under that age, but they are not yet able to say for sure whether that’s because they are higher risk, or whether more young women have been vaccinated.
In Germany, 29 out of 31 patients with the brain clots have been women. But the European regulator has said that may be because countries like Germany began by vaccinating communities like health-care workers, which include more women.
The EMA said that the majority of the blood clots have occurred in women under 60. Whether the risks outweigh the benefits of the vaccine for parts of the population like younger women: “At the moment that is something that is very difficult to answer,” said Straus.
In Britain, regulators are essentially advising that, if possible, those under 30 should receive the Pfizer or Moderna vaccine if available, instead of taking the AstraZeneca jab.
The U.K. vaccine advisory body and medicines regulators said that evidence was “firming up” that the AstraZeneca shot might be causing these very rare clots.
June Raine, head of the Medicines and Healthcare Products Regulatory Agency, said as of the end of March, more than 20 million people in Britain had received at least one dose of AstraZeneca. 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.
Raine said that 4 people in a million may have died as a result of a clot from the AstraZeneca vaccine.
The health officials stressed that the investigation into the causal links between vaccination and clots was ongoing and not yet definitive.
They pressed that for most people — especially the elderly — it is far better to get any safe and effective vaccine than not. The British officials said they were making new recommendations out of an “overabundance of caution.”
“This is a course correction,” said Jonathan Van-Tam, England’s deputy chief medical officer, at a televised briefing. 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 — of getting a clot from the AstraZeneca vaccine as “vanishingly small.”
“This vaccine has proven to be highly effective in preventing severe disease and hospitalization, and it is saving lives,” said EMA chief Emer Cooke. “Vaccination is extremely important in helping us in the fight against covid-19 and we need to use the vaccines.
Booth reported from London.