latest outbreak of Ebola virus in west Africa is the worst ever—as of
Monday, it had infected more than 1,200 people and claimed at least 672
victims since this spring. Guinea, Liberia and Sierra Leone all have
An official at Doctors Without Borders has declared the outbreak as “totally out of control,” according to NBC News.
Unfortunately, doctors have no effective vaccines or therapies. Health
care workers can only attempt to support patients’ immune systems
(regulating fluids, oxygen levels, blood pressure and treating other
infections) to help the afflicted fight off the virus as best they can.
A vaccine to help battle future Ebola outbreaks may be just a few years
away, however. During the past decade researchers have made significant
progress, and vaccines have worked in nonhuman primates.
it has been hard to raise money for human safety tests. To learn about
the latest advances as well as obstacles, Scientific American spoke to
Thomas Geisbert, a virologist in the Department of Microbiology and
Immunology at The University of Texas Medical Branch at Galveston. He’s
studied the Ebola virus since 1988 and is currently involved in vaccine
research and development.
[An edited transcript of the interview follows.]
Are there any promising vaccines in development for the Ebola virus?
There are quite a few preventative vaccines in development, with three
to five that have been shown to completely protect nonhuman primates
against Ebola. Some of these vaccines require three injections or more
and some require just a single injection. Most of them are being funded
by the U.S. government, so they’re in various stages of development, but
none of them are ready to be licensed.
The hang-up point with
these vaccines is the phase I trials in humans. That’s where scientists
get frustrated because we know these vaccines protect animals and we
don’t quite understand the regulatory process of why things can’t move
faster. I can’t give you an answer as to why it’s taking so long.
Why doesn’t the human immune system fight the virus off?
The Ebola virus is usually transmitted by close contact and the first
cells it affects are cells important to your primary immune
response—monocytes, macrophages and dendritic cells. These cells are
important because they’re the first to recognize that something foreign
has entered your body and the first cells to trigger your innate immune
system to fight off the infection. This makes it hard to mount an
effective immune response against the virus—your body has a tough time
fighting the virus off, and the virus multiplies to the point that it
takes over major organs in your body.
Can a vaccine counteract these effects?
I’ll give you an example of how a vaccine might work. The vaccine VSV
is probably one of the most promising, and it’s based on a viral vector
related to the rabies virus. It’s a bullet-shaped particle, and on its
surface is a structural protein called a “glycoprotein,” which allows a
virus to recognize a host cell, bind to it and take over the host cell’s
machinery. With a vaccine, we remove the gene that encodes the
glycoprotein of the VSV virus and we replace it with a gene that encodes
the glycoprotein of Ebola. You end up with a vaccine that has an Ebola
glycoprotein on the surface. Now, it doesn’t behave like Ebola because
the rest of its genome is not Ebola, but because it has the Ebola
glycoprotein your body is going to recognize it as foreign and build up
an immune response against Ebola.
How far along in development is the VSV vaccine?
It’s at the point now where we’re trying to get the funds to do the human studies.
What are the biological challenges of developing a vaccine for Ebola?
There are some vaccines that are “replication defective,” meaning they
don’t replicate, and they tend to be safer. Then there are other
vaccines that are more efficacious, but they’re “replication competent.”
An example of the latter would be the measles vaccine or yellow fever
vaccine. They’re usually crippled, so they’re not as dangerous as a wild
type virus but certain people could have an adverse event when given a
vaccine that’s replication competent.
vaccines may only require a single injection whereas with the
replication-defective vaccines you might have to get boosters every
year, because they’re not as efficient. So do you go for a vaccine that
protects humans in a single injection? In Africa you almost have to,
because in an area like that you’re lucky to get someone into a clinic
to be vaccinated once. It’s a trade-off—efficacy versus safety. That’s
one of the biggest challenges.
Can you give an estimate for when we might have an effective Ebola virus vaccine?
My guess is anywhere from two
to six years. I hate to say this, but it really depends on financial
support for the small companies that develop these vaccines. Human studies are expensive and require a lot of government dollars. With
Ebola, there’s a small global market—there’s not a big incentive for a
large pharmaceutical company to make an Ebola vaccine, so it’s going to
require government funding.
I would like to see a
situation where we tried to advance our lead candidate vaccines as fast
as we can to get phase I studies done. I think we should start with the
first responders—the health care workers in areas of high risk. This
outbreak is so unique because it’s occurring in an area we’ve never seen
it before and also because it seems there’s a higher percentage of
medical staff infected than we’ve seen before. I’ve seen all of these
vaccines work in numerous animals and I’ve never seen an adverse event
from them. I appreciate the safety concerns but it would be great if
there were some way to fast-track this. People are being exposed to
Ebola and there’s a 60 to 90 percent chance they’re going to die—I think
we have to look at it in this context.
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