An Indian child is administered polio vaccine in Kolkata, India, Sunday, June 17, 2012.
Photograph by: AP-Bikas Das , THE CANADIAN PRESS
Public health officials plotting
the strategy behind the effort to rid the world of polio are seeking approval
for fundamental changes to the blueprint for the way the eradication program
will eventually come to a stop. The Global Polio Eradication
Initiative is asking for endorsement of changes it wants to make to the polio
endgame, the tricky manoeuvring that will be needed to safely stop vaccinating
against polio once it appears the viruses are no longer spreading and causing
disease.
The initiative hopes the options
it is proposing will speed up the end of polio transmission and make the final
moves in this lengthy battle safer. At a meeting in Geneva today, it is asking
the World Health Organization's vaccine experts — the Strategic Advisory Group
of Experts on Immunization — to approve recommendations aimed at making
injectable polio vaccine a more crucial component of the endgame strategy.
Getting a green light from the
committee, which goes by the acronym the SAGE, is only the first step in an
approval process that would require countries to sign on as well. And the WHO's
point person for polio knows all countries aren't there yet when it comes to
agreeing to a role for injectable vaccine, or IPV as it is known. "I think
we have to accept that we are not at a point yet where every country has
concurred to introduce this universally. Not at all," Dr. Bruce Aylward,
the assistant director-general for polio, emergencies and country collaboration
said in a recent interview.
Since the polio eradication
program was launched in 1988 it has relied on oral polio vaccine. OPV, in polio
shorthand, costs pennies a dose and is easy to administer. Anyone can be
trained to give the vaccine, two drops of which are squeezed from a eye dropper
into an open mouth. It is given to millions of children in scores of countries
every year.
By comparison, the injectable
vaccine is substantially more expensive, currently running at around $2.75 a
dose when procured through UNICEF, which buys in bulk for developing countries.
(Children immunized with injectable vaccine need three or four doses each.) And
the $2.75 is just the cost of the vaccine. Factor in the syringes and the
medical professionals needed to wield them, and it becomes clear why for many
years IPV was only used by well-to-do countries. Of late, though, an increasing
number of middle-income countries have been using it as well. That's because
despite its higher price, IPV is safer than the oral vaccine, which is made
from live but weakened polio viruses.
OPV causes polio in a small
portion of children who get the vaccine or encounter the viruses used in the
serum. It is estimated that one out of every 750,000 children will develop
polio after getting their first dose of OPV. That is called vaccine-associated
paralytic polio or VAPP.
And the vaccine viruses, which
inoculated children shed in their stools, can spread in an environment where
sanitation is poor, moving from vaccinated child to unvaccinated child in
tainted water or tiny bits of fecal matter picked up on a finger that finds its
way into a mouth. If those vaccine viruses spread long enough, they regain
their power to paralyze, acting like regular polio viruses. Polio cases caused
by spreading vaccine viruses are called VDPVs — vaccine-derived polio viruses. When
wild polio viruses paralyzed scores of thousands of children a year, the
benefits of oral vaccine over rode the risks of VAPP and VDPV cases.
But so far this year there have
only been 177 cases of paralytic polio, in four countries. When the world gets
down to a few dozen of cases of polio a year, the continued heavy reliance on
OPV will risk seeding the world with vaccine viruses that could spread and
trigger outbreaks of VDPV cases. In essence, the question is: When is it no
longer safe to fight fire with fire? Some experts have been saying for years
that injectable vaccine has to play a role in the phasing out of oral vaccine.
And for years the polio campaign leadership resisted those calls, saying the
scientific evidence was not there to support the move.
These days, though, they are IPV
converts. And they are asking the SAGE to urge that all countries vaccinate all
vulnerable children with at least one dose of injectable vaccine as part of the
endgame strategy. The thinking is that if vaccine viruses start spreading more
broadly in the phasing out of the oral vaccine, children will have some
protection from the dose of IPV. Aylward suggested an outbreak of
vaccine-derived polio in Nigeria that started in 2005 has shaped thinking about
the risk vaccine viruses pose. So far there have been 381 cases of paralytic
polio in that outbreak, which has not yet been extinguished. "There's
increasing evidence that these things are real. They can persist and take some
time to knock out. And Africa may be at the greatest risk due to the gaps in
immunization coverage there," he said. It's know that vaccine viruses
spread best in areas where the percentage of children who are fully immunized
is low.
But 24 years into the eradication
effort, many countries are eager to stop spending money on polio vaccination
entirely. Earlier this year, in fact, Bangladesh debated whether it could cut
its national immunization day, a cornerstone of polio control efforts. (The
government was urged not to and it followed the advice.) Aylward said the polio
campaign partners are working hard to find a way to get the price of injectable
vaccine below $1 a dose and ideally closer to 50 cents a shot. At that rate,
more countries would buy into the IPV plan, he said.
Options on the table include
using a smaller dose but injecting it into the skin, rather than the muscle,
because that triggers a better immune response, or using a boosting compound
called an adjuvant with the vaccine to allow for smaller doses. "The issue
now is making sure that there are affordable products available but then also
that countries will accept to do that," Aylward said. "Because there
are a lot of countries that wish they could just stop OPV cold."
The polio eradication campaign is
a partnership of Rotary International, the WHO, UNICEF, the U.S. Centers for
Disease Control and the Bill and Melinda Gates Foundation. It currently hopes
to halt the spread of polio in the three countries which have never stopped
transmission — Nigeria, Pakistan and Afghanistan — by 2014-15. (The fourth
country to report cases this year is Chad, which has seen sporadic importations
of polio from Nigeria.) If that goal is reached, the world would be declared
polio free three years after the last case occurred.
Source: Canada.com
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