Scimex: An experimental Ebola vaccine appears to work after it proved highly protective against the deadly virus in a major trial in Guinea. The vaccine, made by Merck, Sharpe & Dohme, is the first to prevent infection from one of the most lethal known pathogens, and the findings add weight to early trial results published last year. The vaccine, called rVSV-ZEBOV, was studied in a trial involving 11,841 people in Guinea during 2015. Among the 5,837 people who received the vaccine, no Ebola cases were recorded 10 days or more after vaccination. In comparison, there were 23 cases 10 days or more after vaccination among those who did not receive the vaccine. The trial was led by the World Health Organization, together with Guinea’s Ministry of Health and other international partners.
An experimental Ebola vaccine was highly protective against the
deadly virus in a major trial in Guinea, according to results published
today in The Lancet. The vaccine is the first
to prevent infection from one of the most lethal known pathogens, and
the findings add weight to early trial results published last year. 
vaccine, called rVSV-ZEBOV , was studied in a trial involving 11,841
people in Guinea during 2015. Among the 5,837 people who received the
vaccine, no Ebola cases were recorded 10 days or more after vaccination
. In comparison, there were 23 cases 10 days or more after
vaccination among those who did not receive the vaccine.
The trial was led by the World Health Organization, together with Guinea’s Ministry of Health and other international partners.
these compelling results come too late for those who lost their lives
during West Africa’s Ebola epidemic, they show that when the next Ebola
outbreak hits, we will not be defenceless,” said Dr Marie-Paule Kieny,
WHO’s Assistant Director-General for Health Systems and Innovation, and
the study’s lead author .
The vaccine’s manufacturer, Merck,
Sharpe & Dohme, this year received Breakthrough Therapy Designation
from the United States Food and Drug Administration and PRIME status
from the European Medicines Agency, enabling faster regulatory review of
the vaccine once it is submitted.
Since Ebola virus was first
identified in 1976, sporadic outbreaks have been reported in Africa. But
the 2013-2016 West African Ebola outbreak, which resulted in more than
11,300 deaths, highlighted the need for a vaccine.
The trial took
place in the coastal region of Basse-Guinée, the area of Guinea still
experiencing new Ebola cases when the trial started in 2015. The trial
used an innovative design, a so-called “ring vaccination” approach - the
same method used to eradicate small pox.
When a new Ebola case
was diagnosed, the research team traced all people who may have been in
contact with that case within the previous 3 weeks, such as people who
lived in the same household, were visited by the patient, or were in
close contact with the patient, their clothes or linen, as well as
certain “contacts of contacts”. A total of 117 clusters (or “rings”)
were identified, each made up of an average of 80 people.
rings were randomised to receive the vaccine either immediately or
after a 3-week delay, and only adults over 18 years were offered the
vaccine. After interim results were published showing the vaccine’s
efficacy, all rings were offered the vaccine immediately and the trial
was also opened to children older than 6 years.
In addition to
showing high efficacy among those vaccinated, the trial also shows that
unvaccinated people in the rings were indirectly protected from Ebola
virus through the ring vaccination approach (so-called “herd immunity”).
However, the authors note that the trial was not designed to measure
this effect, so more research will be needed.
“Ebola left a
devastating legacy in our country. We are proud that we have been able
to contribute to developing a vaccine that will prevent other nations
from enduring what we endured” said Dr KeÏta Sakoba, Coordinator of the
Ebola Response and Director of the National Agency for Health Security
in Guinea .
To assess safety, people who received the vaccine
were observed for 30 minutes after vaccination, and at repeated home
visits up to 12 weeks later. Approximately half reported mild symptoms
soon after vaccination, including headache, fatigue and muscle pain but
recovered within days without long-term effects. Two serious adverse
events were judged to be related to vaccination (a febrile reaction and
one anaphylaxis) and one was judged to be possibly related
(influenza-like illness). All three recovered without any long term
It was not possible to collect biological samples from
people who received the vaccine in order to analyse their immune
response. Other studies are looking at the immune response to the
vaccine including one conducted in parallel to the ring trial among
frontline Ebola workers in Guinea.
“This both historical and
innovative trial was made possible thanks to exemplary international
collaboration and coordination, the contribution of many experts
worldwide, and strong local involvement,” said Dr John-Arne Røttingen,
director of the Division of Infectious Disease Control at the Norwegian
Institute of Public Health, and the chairman of the study steering group
In January, GAVI, the Vaccine Alliance provided US$5 million
to Merck towards the future procurement of the vaccine once it is
approved, prequalified and recommended by WHO. As part of this
agreement, Merck committed to ensure that 300,000 doses of the vaccine
are available for emergency use in the interim, and to submit the
vaccine for licensure by the end of 2017. Merck has also submitted the
vaccine to WHO’s Emergency Use and Assessment Listing procedure, a
mechanism through which experimental vaccines, medicines and diagnostics
can be made available for use prior to formal licensure.
studies are ongoing to provide more data on the safety of the vaccine
in children and other vulnerable populations such as people with HIV. In
case of Ebola flare-ups prior to approval, access to the vaccine is
being made available through a procedure called “compassionate use” that
enables use of the vaccine after informed consent. Merck and WHO’s
partners are working to compile data to support license applications.
rapid development of rVSV-EBOV contributed to the development of WHO’s
R&D Blueprint, a global strategy to fast-track the development of
effective tests, vaccines and medicines during epidemics.