PARIS, April 5, 2021 (BSS/AFP) – Persistent questions on whether rare but
serious blood clots among those getting the AstraZeneca jab against Covid-19
are more frequent than in the general population, and what causes them if
they are, have continued to undermine confidence in the beleaguered vaccine.
The European Medicines Agency — which has said that benefits outweigh
risks such that the vaccine should remain in use — will provide an updated
assessment next week.
– What has been observed?
The blood clots seen in a handful of people vaccinated with AstraZeneca are
described by the French Medicines Agency (ANSM) as “highly untypical”.
“This thrombosis of large veins is unusually located in the brain, and even
more rarely in the digestive tract,” the agency commented.
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 stop or prevent bleeding.
In mid-March Germany’s medicines regulator, the Paul Ehrlich Institute
(PEI), was the first national health authority to flag what they described as
an aberrantly high number of cases involving these rare cerebral blood clots,
mostly in younger and middle-aged women.
According to some specialists, this set of symptoms pointed to so-called
disseminated intravascular coagulation (DIC), in which blood clots form
throughout the body.
Also seen in extreme cases of sepsis, this condition involves “both
thrombosis and haemorrhaging”, Odile Launay, a member of the scientific body
advising the French government on Covid-19 vaccines, told AFP.
– Link with the vaccine?
“A causal link with the vaccine is not proven but is possible, and further
analysis is continuing,” the EMA said last week.
The agency is scheduled to meet on the question from April 6-9. Other
specialists were more categorical.
“We have to stop speculating on whether there is a link or not — all the
cases showed these symptoms three to 10 days after inoculation with the
AstraZeneca vaccine,” Pal Andre Holme, who heads a team at Oslo National
Hospital working on these cases, told Norwegian television.
“We have not found any other triggering factor.”
Norway’s national medicines agency backed this assessment, with one of
their executives, Steinar Madsen, saying “there is probably a link with the
vaccine”.
For its part, France’s ANSM — pointing to “the very unusual type of
thrombosis, a similar clinical profile, and similar timing of onset” — said
there was a “small” risk.
– How big is the risk?
As of March 31, the EMA identified 62 cases of cerebral venous sinus
thrombosis (CVST) in the world — 44 of them in Europe — among 9.2 million
doses of AstraZeneca administered.
Of those, 14 have resulted in death, though it is not possible to
definitively attribute fatalities to this rare form of thrombosis, the head
of the EMA, Emer Cooke, said last week in a videoconference.
The statistics, she added, are comprehensive, or close to it.
In Germany, there have been 31 suspected cases of CVST — 19 accompanied by
a drop in blood platelets — with nine deaths, according to the Paul-Ehrlich
Institute.
These cases were spread across 2.8 million AstraZeneca vaccine doses
injected, or just over one case per 100,000 doses.
The comparable 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 has been administered more than in any other
country — registered 30 cases as of Saturday, including seven fatalities,
across a total of 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 percent safe but they don’t
exist,” Adam Finn, a professor of paediatrics at University of Bristol, told
the London-based Science Media Centre last week, commenting on renewed bans
of the AstraZeneca vaccine in Germany and elsewhere.
“Right now the biggest risk to our lives and livelihoods throughout the
world is Covid-19,” Finn added. “We need to stay focussed 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 EMA 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 in statement on March 31. – Risk factors?
Most cases of cerebral thrombosis have occurred in those under 65, but it
is impossible to draw any conclusions about age because the vaccine has been
administered to date mostly among younger populations.
The fact that a majority of cases have been among women may simply reflect
the fact the health sector — predominately women — was 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 EMA said.
Notwithstanding, after some countries temporarily paused the AstraZeneca
jab in mid-March, several countries have now suspended the vaccine again.
Germany decided last week to ban its use for anyone under 60, while in
Canada — as in France — the age threshold is 55. In Sweden the age cutoff
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 have taken the more radical step of suspending the
AstraZeneca vaccine altogether.
– Possible explanations?
For the moment, there are only hypotheses, though the EMA is expected to
suggest next week which are the more likely.
In a study released on March 28 that has not yet been peer-reviewed, German
and Austrian researchers pointed to a known biological mechanism as a
possible 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)”.
HIT is a rare and serious reaction of the immune system to the anti-
coagulant medication 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 (VIPIT).”
Researchers at Oslo National Hospital had earlier suggested that cases
might have been triggered by a “powerful immune response” to the vaccine.
An association of French scientists and doctors called “On the Side of
Science” have said such an immune response could come from the accidental
insertion of the needle into a vein in the upper arm, rather than muscle.