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 Initial results from the trial, which tested Merck <MRK.N> and
NewLink Genetics’ <NLNK.O> VSV-ZEBOV vaccine on some 4,000 people
who had been in close contact with a confirmed Ebola case, showed
complete protection after 10 days.
The results were described as "remarkable" and "game changing" by
global health specialists.
"We believe that the world is on the verge of an efficacious Ebola
vaccine," WHO vaccine expert Marie Paule Kieny told reporters in a
briefing from Geneva.
The vaccine could now be used to help end the worst recorded
outbreak of Ebola, which has killed more than 11,200 people in West
Africa since it began in December 2013.
WHO Director-General Margaret Chan said the results, published
online in the medical journal The Lancet, would "change the
management of the current Ebola outbreak and future outbreaks".
The Gavi Alliance, which buys vaccines in bulk for poor countries
who struggle to afford them, immediately said it would back an Ebola
shot once it is approved.
"These communities need an effective vaccine sooner rather than
later," Gavi's chief executive Seth Berkley said. "We need to be
ready to act wherever the virus is a threat."
This and other vaccine trials were fast-tracked with huge
international effort as researchers raced to test potential
therapies and vaccines while the virus was still circulating.
"It was a race against time and the trial had to be implemented
under the most challenging circumstances," said John-Arne Røttingen
of Norway's Institute of Public Health, chair of the trial’s
steering group.
"RING VACCINATION"
The Guinea trial began on March 23 to evaluate the effectiveness and
safety of a single dose of VSV-ZEBOV using a so-called "ring
vaccination" strategy, where close contacts of a person diagnosed
with Ebola are immunized - either immediately, or at a later date.
As data began to emerge showing the very high protection rates in
those vaccinated immediately, however, researchers decided on July
26 that they would no longer use the "delayed" strategy, since it
was becoming clear that making people wait involved unethical and
unnecessary risk.
The trial is now being continued, with all participants receiving
the vaccine immediately, and will be extended to include 13- to
17-year-olds and possibly also 6- to 12-year-old children, the WHO
said.
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Jeremy Farrar, a leading infectious disease specialist and director
of the Wellcome Trust, said the trial "dared to use a highly
innovative and pragmatic design, which allowed the team in Guinea to
assess this vaccine in the middle of an epidemic".
"Our hope is that this vaccine will now help bring this epidemic to
an end and be available for the inevitable future Ebola epidemics,"
his statement said.
The medical charity Doctors without Borders (MSF), which has led the
fight against Ebola in West Africa, called for VSV-ZEBOV to be
rolled out to the other centers of the outbreak, Liberia and Sierra
Leone, where it says it could break chains of transmission and
protect front-line health workers.
VSV-ZEBOV was originally developed by Canada's public health agency
before being licensed to NewLink Genetics, which then signed a deal
handing Merck the responsibility to research, develop, manufacture
and distribute it.
The success of the Guinea trial is a big relief for researchers,
many of whom feared a sharp decline in cases this year would scupper
their hopes of proving a vaccine could work.
Another major trial in Liberia, which had aimed to recruit some
28,000 subjects, had to stop enrolling after only reaching its
mid-stage target of 1,500 participants. Plans for testing in Sierra
Leone were also scaled back. That left the study in Guinea, where
Ebola is still infecting new victims, as the only real hope for
demonstrating the efficacy of a vaccine.
(Additional reporting by Tom Miles in Geneva and Ben Hirschler in
London; Editing by Kevin Liffey)
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