The UK is prepared to limit use of the Oxford-AstraZeneca Covid-19 vaccine to people over 30 should the medicines regulator change its advice, the country's Vaccines Minister Nadhim Zahawi said.
Channel 4 News said on Monday that the UK’s Medicines and Healthcare Products Regulatory Agency was considering restrictions owing to concerns over blood clots.
“Two senior sources have told this programme that while the data is still unclear, there are growing arguments to justify offering younger people – below the age of 30 at the very least – a different vaccine,” it reported.
MHRA chief executive Dr June Raine said no decision had been made and urged people to continue to get vaccinated.
“Our thorough and detailed review is ongoing into reports of very rare and specific types of blood clots with low platelets following the Covid-19 vaccine of AstraZeneca,” she said.
“No decision has yet been made on any regulatory action.”
Mr Zahawi said the government would follow any advice from the regulator.
“We’ve done over 20 million vaccinations using the Oxford-AstraZeneca vaccine … at the moment, they’ve been very clear to say when you get your invite come forward and get the vaccine,” he told Sky News on Tuesday.
“But we will be led by what the regulator and scientists say is the right thing to do. We stand ready … to implement whatever they decide.”
Questions on whether rare but serious blood clots among those receiving the AstraZeneca injection are more frequent than in the general population, and what causes them if they are, continue to undermine confidence in the vaccine.
The European Medicines Agency said the benefits outweigh the risks, and it will provide an updated assessment next week.
The blood clots in a handful of people inoculated with the vaccine were described by the French Medicines Agency as “highly untypical”.
“This thrombosis of large veins is unusually located in the brain, and even more rarely in the digestive tract,” the agency said.
It is also associated with a condition characterised by abnormally low levels of platelets, which are small cell fragments in our blood that form clots to prevent bleeding.
In mid-March, Germany’s medicines regulator the Paul Ehrlich Institute was the first national health authority to flag what they said was an aberrantly high number of cases involving rare cerebral blood clots, mostly in young and middle-aged women.
Some specialists say these symptoms indicated disseminated intravascular coagulation, in which blood clots form throughout the body.
Also appearing in extreme cases of sepsis, the condition involves “thrombosis and haemorrhaging”, Odile Launay, a member of the scientific body advising the French government on Covid-19 vaccines, told AFP.
“A causal link with the vaccine is not proven but is possible, and further analysis is continuing,” the French Medicines Agency said last week.
The agency was scheduled to start talks on the matter on Tuesday.
Other specialists were more insistent.
“We have to stop speculating on whether there is a link or not,” said Pal Andre Holme, who leads a team at Oslo National Hospital working on these cases.
“All of the cases showed these symptoms three to 10 days after inoculation with the AstraZeneca vaccine. We have not found any other triggering factor.”
Norway’s medicine agency backed his assessment, with one of its executives, Steinar Madsen, saying: "There is probably a link with the vaccine.”
The French agency said that because of “the very unusual type of thrombosis, a similar clinical profile, and similar timing of onset”, there was a “small risk”.
As of March 31, the European agency identified 62 cases of cerebral venous sinus thrombosis in the world – 44 of them in Europe – among 9.2 million doses of AstraZeneca’s vaccine administered.
Of those, 14 have resulted in death, although it is not possible to definitively attribute fatalities to this rare form of thrombosis, head of the agency Emer Cooke said last week.
In Germany, there have been 31 suspected cases of CVST, 19 accompanied by a drop in blood platelets, with nine deaths, the Paul Ehrlich Institute said.
These cases were spread across 2.8 million AstraZeneca vaccine doses injected, or about one case for every 100,000 doses.
The figures for France are 12 cases and four deaths out of 1.9 million doses, and for Norway, five cases and three deaths out of 120,000 doses.
Britain, where AstraZeneca’s shot has been administered more than in any other country, registered 30 cases as of Saturday, including seven deaths, from 18.1 million doses.
But as is true of all medications, risks must always be weighed against benefits.
“We would all prefer to have drugs that are 100 per cent safe but they don’t exist,” Adam Finn, a professor of paediatrics at University of Bristol, told the Science Media Centre in London.
“Right now the biggest risk to our lives and livelihoods throughout the world is Covid-19.
“We need to stay focused on the need to prevent it taking millions more human lives before it is brought under control, and the only effective way to do that is through vaccination.”
The European agency has consistently echoed this view.
“The benefits of the AstraZeneca vaccine in preventing Covid-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects,” it said.
That most cases are among women could reflect the fact that health sector workers, predominately women, were given priority for vaccination.
“At present, the review has not identified any specific risk factors, such as age, gender or a previous medical history of clotting disorders for these very rare events,” the European agency said.
While some countries temporarily paused the AstraZeneca inoculations in mid-March, several countries suspended the vaccine again.
Germany decided last week to ban its use for anyone under 60, while in Canada and France, the age threshold is 55 and in Sweden it is 65.
"We do not have just one vaccine, we have several," Sandra Ciesek, a professor of medical virology at the Goethe University Frankfurt wrote in Science magazine.
“So restricting the AstraZeneca vaccine to older people makes sense to me.”
Norway and Sweden took the more radical step of suspending AstraZeneca’s vaccine altogether.
For the moment there are only hypotheses, although the European agency is expected to suggest next week which are the more likely.
In a study released on March 28 which has not yet been peer-reviewed, German and Austrian researchers indicated that a known biological mechanism could hold an explanation for the apparent surge in atypical thrombosis.
The AstraZeneca vaccine, they wrote, is associated with a thrombosis disorder “that clinically resembles heparin-induced thrombocytopenia”.
HIT is a rare and serious reaction of the immune system to the anticoagulant drug heparin.
The authors, led by Andreas Greinacher from the University of Greifswald, proposed a name for what they described as a new syndrome, “vaccine-induced prothrombotic immune thrombocytopenia”.
Researchers at Oslo National Hospital, meanwhile, suggested that cases might be triggered by a “powerful immune response” to the vaccine.
An association of French scientists and doctors called On the Side of Science said such an immune response could stem from the accidental insertion of the needle into a vein in the upper arm, rather than muscle.
