Barbra
Mahon, CDC STRIVE Lead
By Kemo Cham
[First
published on www.politicosl.com] STRIVE (Sierra Leone Trial to Introduce Vaccine against Ebola) is one of
several trials conducted during the 2014 Ebola outbreak in West Africa. Other
trials were held in Guinea and Liberia which, like Sierra Leone, were seriously
affected by the deadly epidemic that ended up claiming over 11, 000 lives by
the time it was declared over by the World Health Organisation earlier this
year.
Late last month
experts, representing the government of Sierra Leone, the Ministry of Health
and Sanitation (MoHS), the University of Sierra Leone, and the United States
Centers for Diseases Control and Prevention (CDC), converged at the Bintumani
Hotel in western Freetown to celebrate what they termed as a successful study.
Politico talked to Dr
Barbara Mahon [MD, MPH], the CDC’s Lead in STRIVE, on the progress of the study
and its future.
Please read on.
Politico: Late last month you [STRIVE
team] gathered at the Bintumani Hotel. What that was about?
Mahon: That
was a meeting to provide a final update on STRIVE and to share some of the
current high level results. We talked about how SREIVE has completed follow up
of more than 8, 000 volunteers who were vaccinated. There are a few women who
became pregnant after vaccination that are still being followed.
Were these women part of the study?
They were
part of the study, they became pregnant after been vaccinated and we are following
them until they deliver. But the main follow up of the people who were
vaccinated has been completed.
Among those
8, 000 people [there was] no serious adverse event related to vaccination. So
that provides actually the largest safety experience with this vaccine and it
could be really important as part of the compilation of all of the information
on the vaccine so that it can be submitted by the manufacturer for licensing.
You just said some women got pregnant
during the trial. Was that anticipated?
Well, women
were counseled not to become pregnant until two months after vaccination. All
of them had a pregnancy test at the time of vaccination. This is precaution.
There is no known risk but to be cautious they were counseled not to become
pregnant until two months afterwards. As you know sometimes things don’t go as
planned and some did become pregnant and we are following them to see how their
pregnancies are going.
When you said you are following them,
are you looking specifically for something?
They are
being followed until the baby is born and the baby can be examined.
I remember in February 2015, you [STRIVE
team] were part of a team of experts who made a presentation about a planned
vaccine study. Back then it was called the Sierra Leone Ebola Vaccine
Evaluation Study (SLEVES). How are these two related?
I wasn’t
here then and I am not familiar with that acronym. STRIVE is the only study CDC
is sponsoring here.
What vaccine candidate are we talking
about here?
The
technical name is the rvsvZEBOV. This is the vaccine that was shown to be
effective… A trial using the same vaccine was conducted in Guinea and the
preliminary result from that study showed effectiveness against Ebola.
Reports from the Bintumani meeting
cited officials describing the trial as successful. What exactly did you mean?
I think it’s
really important to understand that more than 8, 000 volunteers took the
vaccine and there was no serious adverse events that related to the vaccine in
that entire group of people. So that’s one of the most important results of the
study.
There is
another result that is pending and we expect it to be available in the early
part of next year. And that is a sub
group of the participants in the study who gave blood specimen before they were
vaccinated and a specified time period after they were vaccinated to be tested
for antibodies, the immune response against the vaccine, and so using both
results, it will cast light on the immune response to the vaccine and on the
duration of the protection that might be given by the vaccine.
This is a sub
set of people who not only took the vaccine but also gave blood specimen to
test the effect of the vaccine on the immune system.
I see. Two in one study. Is that it?
Yes, those
people gave information about safety, but they also are going to be giving
information about the body’s immune response to the vaccine.
And this was part of the original
plan of the study?
It was part
of the protocol for the study. The protocol was developed over time and this
became increasingly important as the number of cases of Ebola decreased. It’s
only good that Ebola was controlled in Sierra Leone. But because there were no
Ebola cases in STRIVE participants, STRIVE is not going to be able to show that
the vaccine prevents Ebola. But this immunogenicity study can show that the
vaccine spurred the development of a response that could be protective.
When the 2014-2016 epidemic was
spreading, it made sense to conduct a study like this, because there were test
cases which we know are needed for such. Now there are no test cases. What does
this mean for the study?
In the Guinea
study with the same vaccine there were test cases. And so they were able to
demonstrate a decrease in Ebola cases. What STRIVE adds to that is the large
safety experience as well as the ability to measure the immune response to the
vaccine. So you put it all together, all of that information will be part of
the application for licensing.
And the Guinea study is a part of the
Sierra Leone study?
No, the
Guinea study is a separate study, sponsored by WHO, conducted in collaboration
with Guinean colleagues.
I mean was it the same vaccine?
Yea, it’s
the same vaccine. There is a third study in Liberia that’s called PREVAIL that
also included the same vaccine, as well as another vaccine.
And at the end of the day, approval
will take account of all these results?
Yes.
The fact that Ebola was waning was a concern,
wasn’t it?
Well, from a
very narrow point of view of the study, it limited the ability to demonstrate
disease prevention from the vaccine.
We can never
call waning Ebola a problem, it’s a good thing. I can’t even say that… It’s only
good. And STRIVE is still able to provide this really important information.
I understand studies were conducted outside
West Africa on the same candidate vaccine. Is that so?
This vaccine
has been studied in volunteers in many countries, in Africa, in Europe, in the
United States… It wasn’t the exact same trial, but the vaccine has been used
widely in volunteers from many countries.
These were before the 2014 outbreak?
Before and
after.
The relationship between the trials
in Sierra Leone and Guinea is now quite clear. In the other countries, what was
it looking at?
All of the
studies used slightly different scientific approaches but all were attempting
to show an effect on the disease and to gather information on safety. And I
believe that they all included measurement of antibodies. The different studies
ultimately will provide different information on the vaccine that can be used
to support the application for licensing.
STRIVE is funded by US government,
but who actually owns this particular candidate vaccine?
It’s owned
by Merck [Pharmaceutical Company] with licensing from another company. Merck is
the manufacturer.
How is the rvsvZEBOV different from
other candidate vaccines?
It’s what is
called a vector vaccine, meaning that a small piece of Ebola virus that cannot
cause Ebola is inserted into a different virus that’s harmless. Other vaccines have
taken a different approach using different vectors and other difference
approaches.
We were told that in this trial you are
not using placebos. Please explain that.
There was a
great deal of thought and discussion about the design of the study and whether
to use placebos or not… It think it will be fair for me to say that there was a
concern that those people who received a placebo might falsely assume that they
were protected and might not be as careful in protecting themselves from Ebola
using PPEs (Personal Protection Equipment) and using appropriate precautions in
the hospitals.
We know that this [study] is a
collaboration between the MoHS, the University of Sierra Leone and the CDC.
Please tell us the specific role of each party in this.
COMAHS [College
of Medicine and Allied Health Sciences] is the lead for the study. Dr [Mohamed]
Samai is principal investigator. And COMAHS is involved in every aspect of implementation
of the study. CDC is the sponsor. CDC has played a more active role in
supporting COMAHS than a sponsor often does, in recognition that this sort of
activity is new for Sierra Leone, to build capacity, exchange information, and
so forth.
So CDC has
been very involved as well in supporting COMAHS in implementation.
The Ministry
of Health from the start directed CDC to work, first and foremost, with COMAHS because,
of course, their attention had to be primarily focused on response to Ebola.
But they have also been involved in reviewing protocol and approving human subject
protection and the other aspects of the study. So it really is a three way
partnership.
When you said COMAHS is the lead. I
really will like to know what they do. I am asking because the assumption is
that local expertise, in terms of the technical work, doesn’t exist.
That’s not
so. There is a great deal of talent and knowledge of clinical studies. Dr Samai
is an experienced expert investigator and there are others. But you are right,
capacity is limited here and so CDC has done what we can to support with
technical assistance, to support with training as needed and to be available
for consultation.
Initially, during the launch of the
study back last year, we were also told that 6, 000 people were to participate.
Now the number has gone to 8, 000. How did that happened?
Because Ebola
was decreasing, there was a time when it appeared that if more people were
involved there might still be the opportunity to demonstrate an effect against
the disease. So protocol amendment was written and submitted for ethical
review, human subject review, in Sierra Leone and in the US and the increase
was approved, in part because at that point there was some information on
safety and the experience at that point had been very good.
There are no studies like this that
don’t come with side effects, although you have indicated there were no serious
adverse events. But what are the instances have you had to deal with?
It’s really
important to be clear on this. There were no serious adverse events, which
means serious adverse events related to the vaccine. And so there was no
hospitalization, no deaths, no events that would cause a permanent disability,
and so forth.
The vaccine
does cause reactions, it causes muscle pains, headache, fever, it can cause
aches in the joints, and the events that we saw here in Sierra Leone…many
people experienced those. They got better on their own within one to two days
and they were not serious adverse events. They didn’t lead to hospitalization.
They didn’t lead to more serious outcomes.
So
absolutely the vaccine can cause some vaccine reactions, as what all vaccines
do. But thankfully we didn’t see any serious response that were related to the
vaccine.
Profile of Dr Mahon from the CDC
Dr Mahon received her MD
and clinical training in pediatrics from the University of California, San Francisco
and her MPH from the University of California, Berkeley. She trained in CDC’s
Epidemic Intelligence Service (EIS). Dr. Mahon is deputy chief of the Enteric
Diseases Epidemiology and
Surveillance
Branch at the Centers for Disease Control and Prevention (CDC). The branch is
responsible for national surveillance for enteric diseases. It conducts
epidemiologic studies of the burden, trends,
and
food source attribution of foodborne diseases caused by
Listeria,
Salmonella, and E. coli O157, among other pathogens. The branch’s work also
focuses on vulnerable populations, including older
adults,
young children, and other groups, with the goal of creating knowledge needed to
protect people by preventing disease. Dr. Mahon has a broad background in
infectious disease epidemiology, having
worked
on foodborne diseases, vaccine - preventable diseases, and sexually transmitted
diseases in academic and industry positions as well as in government.
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