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
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