A highly unusual
clinical trial in Guinea has shown for the first time that an Ebola
vaccine protects people from the deadly virus. The study, published
online today by The Lancet, shows that the injection offered contacts of
Ebola cases 100% protection starting 10 days after they received a
single shot of the vaccine, which is produced by Merck. Scientists say
the vaccine could help to finally bring an end to the epidemic in West
Africa, now more than 18 months old.
"This will go down in
history as one of those hallmark public health efforts," says Michael
Osterholm, the director of the Center for Infectious Disease Research
and Policy in Twin Cities, Minnesota, who wasn't involved in the study.
"We will teach about this in public health schools."
"It's a wonderful result
and a fantastic illustration of how vaccines can be developed very
quickly and can be used in an outbreak situation to control the
disease," says Adrian Hill, a vaccine researcher at the University of
Oxford in the United Kingdom, also not involved in the work.
The vaccine, first
developed by researchers at the Public Health Agency of Canada, consists
of the Vesicular Stomatitis Virus (VSV), which causes disease in
livestock but not people, with the Ebola surface protein stitched into
it. It is one of two vaccines currently being tested in the
Ebola-stricken countries; the other one is produced by GlaxoSmithKline
(GSK). The study of the Merck vaccine was led by Ana Maria
Henao-Restrepo of the World Health Organization (WHO) in Geneva,
together with colleagues at the Norwegian Institute of Public Health in
Oslo, the Guinean Ministry of Health, and others.
The decision to start
the trial was taken in October, but it didn't get off the ground until
March. By then, Ebola cases had already begun to plummet, and they were
scattered across a large area in Guinea. To show efficacy in a standard
randomized controlled trial, the researchers would have had to enroll
far more people than was feasible.
Instead, they opted for a
design called ring vaccination, in which only contacts of new Ebola
patients, as well as the contacts' contacts, were vaccinated. The rings,
or clusters, were randomized; in 48 of them, vaccination occurred as
soon as possible after the detection of the Ebola case in their
community. In the 42 other clusters, the vaccination teams came to give
the shots three weeks later. The researchers then counted the number of
new Ebola cases in each ring; because they weren't sure how long it
takes for the vaccine's protection to kick in, they only included cases
that occurred at least 10 days after vaccination in their primary
analysis of the data. There were zero such cases among the 2014 people
who were vaccinated right away, and 16 among the 2380 who got the shot 3
weeks later. That translates to 100% vaccine efficacy, at least in this
study, the researchers write.
The idea of a ring
vaccination design, never before used in a formal vaccine study, "was
absolutely very creative," says Osterholm, and it allowed the team to
follow the epidemic wherever it went. "Had this been a standard,
straightforward randomized controlled trial, we would never had this
answer.”
"It surprised me how
quickly you can intervene with a vaccination and have an effect," says
Jeremy Farrar, the head of the Wellcome Trust research charity, which
co-funded the study. "It’s possible to do that sort of complex work in
very, very complex environments—ethically, socially, culturally and
scientifically. You can do it. That is a revelation for many people."
Source: Sciencemag.org
