THE QUEST TO ERADICATE
POLIO IN ENDEMIC COUNTRIES
Change and challenge is in the wind as 2008 comes to an
end. The same is true when examining this month's ReachMD XM 160 special
series - Focus on Global Medicine. We take a look at both the changes and the
challenges impacting global medicine.
Nearly 90% of poliomyelitis cases are found in Nigeria and
India, two countries where the virus remains endemic. Poor vaccine coverage
especially in Nigeria has contributed to the transmission of disease. Could a
newly licensed monovalent vaccine help eliminate the virus in the region? Is
this strategy applicable in India as well and how does it all fit into the
worldwide effort to eradicate poliovirus? You are listening to ReachMD, The Channel
for Medical Professionals. Welcome to a special segment - Focus on Global
Medicine. I am your host, Dr. Jennifer Shu, Practicing General Pediatrician
and Author. Our guest is Dr. Bruce Aylward, Internist, Epidemiologist, and
Director of the Global Polio Eradication Initiative with the World Health
Organization in Geneva, Switzerland.
DR. JENNIFER SHU:
Welcome Dr. Aylward.
DR. BRUCE AYLWARD:
Thank you Jennifer.
DR. JENNIFER SHU:
Nigeria and India are among the handful of remaining
countries that are endemic in polio. What are the challenges that have made it
so difficult to eradicate the virus in these countries?
DR. BRUCE AYLWARD:
Jennifer, you probably know when we set off to eradicate
polio about 20 years ago, there were over 125 countries where the disease was
still endemic, and over the course of the past 20 years, the disease has been
eliminated from all except 4 of those countries indigenous polio has been
eliminated, and in addition to India and Nigeria, there is Pakistan and
Afghanistan which have also had persistent transmission despite 10 years of
ongoing eradication activities in each of these countries. But the reasons for
the ongoing polio in each country and hence the potential solutions are quite
different. In Nigeria it appears to simply be the fact that not enough kids
are getting vaccinated in the northern part of the country as simple service
delivery or suboptimal delivery of the vaccines seems to be the problem. In
northern India, interestingly, a very different challenge, what it seems there
is we are dealing really with a two-pronged problem. One is because of the
density of population, poor sanitation, etc. we have got incredibly efficient
transmission of the virus, the virus can just circulate so easily in that
area. The other problem we have is we found and this is one of the important
findings that came out of the research at the end of the program in the last
couple of years is that the efficacy of the vaccine in northern India and the
last two infected areas of India is fully half of what it is, the per dose
efficacy in the rest of the country. So, we have more of a technical problem
to solve in India and an operational challenge in Nigeria.
DR. JENNIFER SHU:
You brought up a number of very important points. Let's try
to break it down a little bit and talk a little bit in more detail about
specifics. First of all, why is it that these two countries play such as large
role in global polio eradication? Is it just because of the sheer numbers, or
is there transmission of the poliovirus from these countries to others?
DR. BRUCE AYLWARD:
It’s a two-pronged problem, multi-facet problem both of
these countries pose for the eradication initiative. First is the sheer burden
of disease together they account for 90% of the polio in the world and the
second thing is that these are the only two countries in the world that have
served as the virologic origins so to speak of all of the international spread
of polio that we have seen in the last 5 to 6 years. In the last 5 years
alone, if I remember correctly, we have seen over 100 documented exportations
of polio out of these 2 countries, 75% of it out of Nigeria and the balance
from India, and it has caused over 500 million, now nearly three-quarters of a
billion dollars in international control efforts to deal with the spread of
polio from these countries. So, there is a problem within the countries
themselves and the international spread from them. Afghanistan and Pakistan
are different. In both those countries, the virus has traveled back and forth
across their border, but it actually hasn't spread outside of those areas.
DR. JENNIFER SHU:
I was looking at your website recently and there is a report
on the number of global cases by country, and I noticed that in 2008, there was
a higher number of cases for many of these endemic countries than in recent
previous years. What you think might be the reason for that?
DR. BRUCE AYLWARD:
Well, in each country it’s a little bit different. In the
case of India what actually happened was they had a big outbreak in late 2007,
which then carried over into the early part of 2008. So, the vast majority of
the cases you are seeing for India are basically from the first part of this
year and the tailing off an outbreak from last year, and that outbreak was due
to what we called the type III polio virus and it was a consequence of a big
emphasize to try and stop the type I polio first as that was the one that was spreading
internationally. In Nigeria, a different problem. What happened there was
because the immunization campaigns weren’t getting extremely coverage, they
were getting about 70% of children in some of the areas of the north. Over the
past 2 to 3 years, there was an accumulation of susceptible kids and bang a
major outbreak of the type I the particularly dangerous poliovirus. In
Pakistan, a third problem, and this gives you a sense of the complexity of the
different pieces of a puzzle we are trying to juggle to mix my metaphors. In
Pakistan, what you are seeing there is an outbreak but it is due to a different
problem. There with the deterioration in security in the tribal areas
bordering Afghanistan just in the last 6 months as the new government has
really put an emphasis to bring some order to those areas, we have seen a large
movement of people out of the polio-infected areas of Pakistan where we sort of
corned the virus and into the polio-free area of the Punjab, which is the
largest province. So really three very different problems in each of these
countries requiring different solutions going forward.
DR. JENNIFER SHU:
Now let's talk a bit about Nigeria specifically in the New
England Journal of Medicine article that you co-authored. You mentioned that
poliovirus immunization was temporarily suspended in part of Nigeria. Is this
what you are talking about regarding lower vaccine coverage in the northern
region?
DR. BRUCE AYLWARD:
Well, in fact, there was a problem with coverage historically
in the north of Nigeria and this is because of the very weak health services in
the northern part of the country. So, routinely, if you think about routine
immunization may be 20% of children are reached in most of the northern states
in contrast to probably some around 60%-70% in the southern states. But, then
as we used the polio campaigns to try and get over that problem in the northern
part of the country, some people began to question why are they going to search
trouble and it gave rise to a lot of rumors that actually was campaigned to
sterilize children, etc., etc. that lead to the suspension of immunization for
12 months while the northern governors in a couple of states tried to sort out
the issue and there has been some lingering problem with respect to concerns
about the safety of the vaccine, but to be perfectly frank, that has not been
the real rate-limiting step, it has continued to be the weakness of the
infrastructure in the northern part of Nigeria and the lack really of local
ownership by some of the governors in the north and some of the district-level
authorities to just take this in hand and ensure all other kids are
vaccinated. In the couple of states where they have done that, we have seen
tremendous progress.
DR. JENNIFER SHU:
Now New England Journal of Medicine article compared
monovalent type I oral polio vaccine with trivalent vaccine and this was done
in the northern region of Nigeria, I believe, which had 96% of all type I cases
in Nigeria in the year 2006, what were some of the key findings of this
comparison?
DR. BRUCE AYLWARD:
What we are trying to look at here Jennifer was whether or
not the monovalent vaccine might provide us an edge in the eradication
initiative in the north of Nigeria. So, we did a case control study over the
last couple of years to look at the efficacy of this new monovalent vaccine as
opposed to usual trivalent polio vaccine, and what we found is that it works at
least 2 if not 3 times better than the trivalent dose per dose in protecting
children against type I polio and that’s particularly important because the
type I polio has the highest paralytic rate of the remaining 2 serotypes and is
also the one that spreads internationally. So, getting that under control very
quickly is the key and clearly we have a much, much, much, better tool for
doing that with the monovalent product.
DR. JENNIFER SHU:
Now even if the monovalent product is more effective, what
you mentioned in the part of India where there is such viral illness, you are
not going to see that immunity no matter which product you use, the monovalent
or trivalent. So, what might be some ways of getting around this problem with
immunity in India?
DR. BRUCE AYLWARD:
In terms of northern India, the challenge clearly is
suboptimal efficacy of the vaccine and the monovalent vaccine. It performs as
well in northern India as the trivalent vaccine does in the rest of the country
but remember you have got that added problem of highly efficient transmission
in the north which means you have to get even higher coverage, higher
population immunity in the north than you would have to in the south. Now
there is a couple of approaches that have been used to try and achieve this.
One has been to mass campaign the population every month, because between
campaigns there are another half a million children being born in the northern
part of India. So, first thing was the government brought the campaigns close
together, used only the monovalent vaccine and that appeared to be successful.
It stopped the indigence transmission of the type I virus, but the problem is
they got reintroduced and took off again here in the north of India. So, what
the government is now looking at is how else could we boost immunity and what
we are particularly interested in is to give the dose of the inactivated polio
vaccine in addition to the oral vaccine to the youngest kids in the highest
risk areas to see if with that we could build their immunity even more quickly
than we can with the frequent campaigns. By the time children are 3 years of
age, 99.5% of them are protected against polio in northern India. The problem
is getting enough doses into them fast enough and there we need some new ideas
and we are hoping a dose of IPV might help.
DR. JENNIFER SHU:
And how many doses do you anticipate in the series of
immunization?
DR. BRUCE AYLWARD:
Well, its interesting in northern India its hard to say how
many doses any individual child needs to protect against polio, but what the
plan is going forward is to continue using the monovalent vaccine basically
every month in children under the age of 5 years and then using a dose of IPV 6
months apart in the highest risk areas to further boost or close any immunity
gaps among the very young after they have had so many doses of mOPV, and the
plan will be to run that approach right through 2009 and have another look at
it in late 2009, but I would be willing to wager by that time we are not going
to have any more of the type I virus and we are going to be focussed on type
III in India.
DR. JENNIFER SHU:
What point in vaccine-induced immunity might we start seeing
eradication of the disease? Is it there are certain level of vaccine coverage
that is required for that?
DR. BRUCE AYLWARD:
The key issue is not so much the coverage as I am sure you
know but the actual level of population immunity and some of the other
interesting insights we have had from our work with Imperial College to try and
evaluate what's going on in Nigeria and India, is that there are different
levels of immunity appeared to be needed in different areas. In Nigeria, it
appears like transmission stops once you get up around 75% to 80% of the
population protected by vaccination, whereas in northern India and potentially
in parts of Pakistan, you have definitely got to get well over 90% and in
northern India over 95%. So, fully in the setting of northern India, a 15
percentage higher in level of immunity is probably needed than in sub-Saharan
Africa.
DR. JENNIFER SHU:
I would like to thank our guest, Dr. Bruce Aylward. We
have been discussing polio eradication efforts in endemic country.
I am Dr. Jennifer Shu. You have listening to a special
segment – Focus on Global Medicine on ReachMD, The Channel for Medical Professionals.
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