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 AstraZeneca's large, late-stage U.S. trial has remained on hold
since Sept. 6, after a study participant in Britain fell ill with
what was believed to be a rare spinal inflammatory disorder called
transverse myelitis.
The widened scope of the FDA probe raises the likelihood of
additional delays for what has been one of the most advanced
COVID-19 vaccine candidates in development. The requested data was
expected to arrive this week, after which the FDA would need time to
analyze it, two of the sources said.
Effective vaccines are seen as essential to help end a pandemic that
has killed more than one million people worldwide.
The administration of President Donald Trump has pledged $1.2
billion to support development of the AstraZeneca vaccine and secure
300 million doses for the United States. Other leading companies in
the U.S. vaccine race include Pfizer Inc, Moderna Inc and Johnson &
Johnson.
Regulators in the UK, Brazil, India and South Africa have allowed
AstraZeneca to resume its clinical trials there.
The FDA, however, wants to determine whether similar side effects
emerged in trials of other vaccines designed by AstraZeneca's
coronavirus vaccine partner, researchers at Oxford University, the
sources said. That does not mean the agency believes there were
safety issues associated with any of these vaccines, they added.
"It just shows that the FDA is being thorough," said one of the
sources.
Further complicating the situation is that the data requested by FDA
is in a different format than what the U.S. regulator requires, two
of the sources said.
The FDA declined to comment on discussions involving an experimental
product. Oxford did not respond to requests for comment. AstraZeneca,
in a statement, said: "We are continuing to work with the FDA to
facilitate review of the information needed to make a decision
regarding resumption of the US trial."
VIRAL VECTOR
All of the vaccines it wants to review use a modified adenovirus as
vectors to safely deliver genetic material from the target illnesses
- flu, Middle East Respiratory Syndrome, and other diseases - into
the body to stimulate an immune system response to fight future
infection.
While other vaccine developers have used human adenoviruses for such
vaccines, the Oxford researchers chose an adenovirus found in
chimpanzees. They felt this would reduce the likelihood that an
individual's immune system would attack the vector virus due to
prior exposure rather than the intended target.
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Reuters reviewed six research papers that detailed safety data of vaccines using
the engineered chimpanzee adenovirus called ChAdOx1 for diseases including
tuberculosis, prostate cancer and influenza.
In one of those trials, one serious adverse event cited by researchers was
deemed unrelated to the vaccine.
The type of review being conducted by the FDA is generally intended to
scrutinize raw data for other side effects, the sources said.
The U.S. government's effort to speed development of a COVID-19 vaccine - and
promises by Trump that one could be available prior to the Nov. 3 presidential
election - has led to concerns of political interference in the regulatory
process at the expense of safety. The FDA has denied this.
AstraZeneca's vaccine development could also be slowed by a change to its
clinical trial protocols to show that it has met pre-determined safety and
efficacy standards.
Independent safety monitors will conduct their first review of the vaccine's
safety and effectiveness after 75 trial subjects become infected with COVID-19,
up from the original initial review plan after about 40 infections, according to
a Reuters review of protocol documents issued in July and amended in
mid-September.
The safety monitors could decide to stop the trial if the vaccine proves either
highly effective, and therefore should be considered for public use before the
trial concludes, or if serious safety problems appear.
"Safety is likely to have been a major reason" for the change, said Thomas
Lumley, chair of biostatistics at the University of Auckland who was not
involved with the study.
AstraZeneca would not say why it had made the change to its protocol.
(Reporting by Marisa Taylor in Washington and Dan Levine in San Francisco;
Additional reporting by Nancy Lapid; Editing by Michele Gershberg and Bill
Berkrot)
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