Denise grady
04/12/2021 17:34
Clarín.com
Society
Updated 04/12/2021 5:34 PM
New research has identified
unusual antibodies
that appear to have caused, in rare cases, severe and sometimes fatal blood clots in people who received the Covid vaccine made by AstraZeneca.
The precise reason for these
rare
reactions
to the vaccine remains a mystery.
Scientific teams from Germany and Norway discovered that people who developed thrombosis after vaccination had produced antibodies that
activated their platelets
, a component of blood that is involved in clotting.
The new reports add extensive detail to what researchers have already publicly stated about this blood disorder.
Younger people seem
more susceptible
than older people, but the researchers say there are no known pre-existing health problems that predispose people to this unusual reaction.
That is concerning
, they say, because there is no way to know if an individual is at high risk.
Reports of thrombosis have already led several countries to limit the AstraZeneca vaccine to older people or to stop using it altogether.
These cases have been a serious blow to global efforts to stop the pandemic, as AstraZeneca's vaccine - easy to store and relatively inexpensive -
has been a mainstay
of vaccination programs in more than 100 countries.
AstraZeneca vials.
Argentina awaits the arrival of vaccines from that laboratory.
Photo: Ansa
The European Medicines Agency, the regulatory body of the European Union, has repeatedly stressed that
bleeding disorder is rare
and that the benefits of the vaccine far outweigh its risks.
But when a side effect has the potential to be devastating or fatal - such as the stroke linked to this vaccine - some regulators and segments of the public
consider the risk unacceptable
, even though it is extremely rare.
As of Sunday, European regulatory bodies had received reports of
222 cases of this
rare blood clotting
problem
in Britain and the European Economic Area from 30 countries (the European Union plus Iceland, Norway and Liechtenstein).
They said that some 34 million people had received the AstraZeneca vaccine in those countries and that thrombosis problems appeared in about
1 in 100,000 recipients.
European regulators reported that, as of March 22, they had carried out detailed reviews of 86 cases,
18 of which had been fatal.
The safety standard for vaccines is set at a very high level, because they
are administered to healthy people.
The apparently greater vulnerability of young people to this bleeding disorder is especially worrisome, since they have a lower risk than older people of suffering a serious illness from Covid.
These differences indicate that overall, compared to older people, younger people
may have less to gain and more to lose
from the AstraZeneca vaccine.
The AstraZeneca vaccine, which has reported some cases of thrombosis.
Photo: Reuters
Germany, the Netherlands, the Philippines, Portugal and Spain have recommended that the AstraZeneca vaccine be given only to
people over 60 years of age.
Canada and France have limited it to those over 55;
Australia, to those over 50;
Belgium, to those over 56. Great Britain, where the vaccine was developed, has been its strongest advocate, but announced on Wednesday that it would start offering alternative vaccines to those under 30 years of age.
Oxford University, which developed the AstraZeneca vaccine, announced Tuesday that it was
suspending a two-month trial
of the vaccine in children and adolescents in Britain while awaiting guidance from regulators.
Cameroon, Congo, Denmark and Norway have stopped using the vaccine.
Full vaccination with the AstraZeneca vaccine requires two doses, but regulatory bodies in France and Germany have recommended that those under 55 who have received one dose be given
a different vaccine as a second injection.
AstraZeneca's vaccine
is not licensed in the United States
, but the company has said it plans to apply to the Food and Drug Administration (FDA) for permission for emergency use.
The agency declined to comment on this rare bleeding disorder.
On Wednesday, the European Medicines Agency said the vaccine package insert should be revised
to include bleeding disorder
as a "very rare" side effect of the vaccine.
In a statement on its website, AstraZeneca reported that it was "actively collaborating with regulators to implement these changes to product information and is already
working to understand individual cases
, the epidemiology, and the possible mechanisms that could explain these extremely rare events. ".
Published studies
The two new studies were published by The New England Journal of Medicine.
One of them, from Germany, describes eleven patients, including nine women between 22 and 49 years old.
Between five and 16 days after vaccination, one or more clots were detected.
Nine had cerebral venous thrombosis, a clot that blocks a vein that drains blood from the brain.
Some had clots in their lungs, abdomen, or other areas.
Six of the eleven died, one of them from a brain hemorrhage.
Although the majority of the patients were women,
it is not known whether women are more vulnerable
than men.
Many health workers in Germany are women and were among the first to be vaccinated.
One of the patients had pre-existing conditions that affected coagulation.
Andreas Greinacher, one of the authors of the report, said that these conditions most likely played
only a minor role
in the reaction that occurred after vaccination.
He also noted that it was a "likely possibility" that people who suffered thrombosis had
some rare and unknown biological traits
- or "individual cofactors" - that predisposed their immune systems to produce potent and misdirected antibodies in response to the vaccine.
He added that this was "good news" for the general population, which does not have those cofactors.
Vaccination of older adults in Spain with the AstraZeneca vaccine.
Photo: AP
There is "clear evidence" that the AstraZeneca vaccine, in rare cases, leads the body to make antibodies that activate platelets, and that those antibodies cause thrombosis, Greinacher said.
But he added: "We have no way of
predicting who will develop these antibodies
."
So far, his laboratory has only identified about 40 cases out of the 1.4 million people who have received the vaccine in Germany.
If the vaccine alone were the cause of the problem, without individual cofactors, there
would be many more cases
, Greinacher said.
He called the deaths of young people "tragic", but noted that the numbers were small.
"Not vaccinating will lead to many more people with serious complications than those affected by vaccination," Greinacher warned.
The first eleven patients in their study, as well as 17 others with postvaccination thrombosis whose blood was tested,
had the antibodies that activate platelets.
The antibodies caused a condition called
thrombotic thrombocytopenia
, which caused both clots and abnormal bleeding.
The researchers suggested naming the new version identified in these patients as "vaccine-induced immune thrombotic thrombocytopenia," or VITT.
What produces this reaction
Scientists put forward various theories about what triggers this immune reaction.
AstraZeneca's vaccine uses a
chimpanzee adenovirus
to deliver DNA to recipients and elicit an immune response against the coronavirus.
Laboratory studies seem to indicate that the chimpanzee virus or DNA could be causing the problem.
Some researchers have suggested that the bleeding from the injection, mixed with the vaccine, could put platelets in the crosshairs of the immune system.
Greinacher called the theories credible but not proven.
The article described specialized blood tests that can be used to diagnose the disorder and distinguish it from other more common clotting problems not related to the vaccine.
The research team suggested treatment with
a blood product called intravenous immunoglobulin
, which is used to treat various immune disorders.
Greinacher compared the treatment to putting out a fire.
A representation of platelets in blood.
Drugs called anticoagulants can also be given.
But the researchers recommended
not prescribing one of the most widely used, heparin
, because the vaccine-related condition is very similar to a serious reaction that occurs, rarely, in people who receive heparin.
The second report, from Norway, concerned five patients, a man and four women who were healthcare workers aged 32 to 54 years, who developed clots and bleeding
between seven and ten days after
receiving the AstraZeneca vaccine.
Four had severe brain clots and three died.
The first symptoms were severe headaches.
Like the German patients, they
all had high levels of antibodies that could activate platelets.
The Norwegian team also recommended intravenous immunoglobulin treatment.
The researchers said the disorder was rare, but "a new phenomenon with devastating effects for otherwise healthy young adults," and suggested that it was perhaps
more common than previous studies
of the AstraZeneca vaccine
had indicated
.
On Friday, European regulators also reported that they were reviewing reports of a few cases of thrombosis that occurred in people who had received the Johnson and Johnson vaccine.
In the United States, federal agencies are investigating reports of a different type of unusual blood disorder that causes a precipitous drop in platelets and that occurred in a few dozen people who had received the Pfizer-BioNTe ch or Moderna vaccines.
The New York Times. Special
Translation: Elisa Carnelli
PS
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