* Ebola vaccine 100 percent effective in Guinea trial
* WHO chief says vaccine will change the way Ebola is
managed
* Fading epidemic left little time for trial to be concluded
(Adds GAVI vaccine alliance's backing, details on development)
By Kate Kelland and Tom Miles
LONDON/GENEVA, July 31 (Reuters) - The world is on the verge
of being able to protect humans against Ebola, the World Health
Organization said on Friday, as a trial in Guinea found a
vaccine to have been 100 percent effective.
Initial results from the trial, which tested Merck (NYSE:MRK) 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 immunised - 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.
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 centres 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.
ID:nL5N0YX18G
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.