|
 European investigators have put forward one theory that the vaccine
triggers an unusual antibody in some rare cases; others are trying
to understand whether the cases are linked with birth control pills.
But many scientists say there is no definitive evidence and it is
not clear whether or why AstraZeneca's vaccine would cause an issue
not shared by other vaccines that target a similar part of the
coronavirus.
Most of the rare blood clots have been seen in women and most cases
have been reported in Europe. Two cases have been reported in India.
The European Medicines Agency said a preliminary review suggests the
vaccine is not associated with an increase in the overall risk of
blood clots. But it did not rule out an association with rare cases
of blood clots in vessels draining the blood from the brain known as
cerebral venous sinus thrombosis (CVST).
Researchers in Germany and Norway, where some of the cases have been
reported, this week hypothesized that the vaccine could be
triggering an immune response in which the body produces antibodies
that could result in blood clots.
Professor Paal Andre Holme of Norway's Oslo University Hospital,
which treated three healthcare workers with severe blood clots after
they received the AstraZeneca vaccine, told a news conference on
Thursday that "we've made discoveries" that could "explain the
clinical progression of our patients."
Holme warned that the findings were preliminary. "This is only the
beginning of all the research that is being done," he said. He did
not release any data supporting his hypothesis.
A team of German researchers at Greifswald University Clinic on
Friday said they came to a similar conclusion. If proven correct,
there may be a way to treat the condition, the scientists said.
EMA researchers on Thursday said they are undertaking several
investigations to determine whether the rare blood clots might be
linked with the vaccine, or occurring by chance. They noted that
many of the events occurred in younger women.
[to top of second column] |
 CVST, though rare, has been
associated with pregnancy and the use of oral
contraceptives. "That's one of the things that
we will be further investigating in the near
future," said Sabine Straus, chair of EMA's
safety committee.
EMA also intends to investigate whether those
who developed the condition had been infected
previously or at the time of the vaccine with
COVID-19, which can cause blood clots.
Several U.S. vaccine experts remain cautious
about the antibody hypothesis and said the high
level of publicity of the events could be
causing more clinicians to report the condition
than normal, which would make it appear that the
events are related to the vaccine.
AstraZeneca's vaccine has received emergency use
authorization in 70 countries, but it has not
yet been approved in the United States.
The U.S. experts also question why such events
would occur only at increased rates with the
AstraZeneca vaccine and not the vaccines by
Pfizer Inc and BioNTech SE, Moderna Inc, Johnson
& Johnson and Russia's Sputnik V vaccine - all
of which are intended to produce antibodies
aimed at the "spike" portion of the coronavirus
that it uses to enter cells.
Like the J&J and the Sputnik vaccine,
AstraZeneca's uses a non-replicating cold virus
known as an adenovirus to deliver spike proteins
into cells and produce an immune response.
"We'll have to see when (German and Norwegian
scientists) submit a peer-reviewed publication
and the scientific community can review it,"
said Dr. Peter Hotez, a vaccine researcher at
Baylor College of Medicine in Houston. "There's
no reason why the AstraZeneca vaccine would do
this whereas the others, including the
adenovirus-based COVID-19 vaccines, wouldn't."
 (Reporting by Julie Steenhuysen; additional
reporting by Terje Solsvik in Oslo; editing by
Peter Henderson and Leslie Adler)
[© 2021 Thomson Reuters. All rights
reserved.] Copyright 2021 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
Thompson Reuters is solely responsible for this content |
