PHA-Exch> Effort to Defeat Polio Faces Unique Challenges

[Claudio Schuftan]

From: Vern Weitzel <vern at coombs.anu.edu.au>
crossposted from: "[health-vn discussion group]" health-vn at cairo.anu.edu.au
http://www.washingtonpost.com/wp-dyn/content/article/2007/12/24/AR2007122401821.html?referrer=emailarticle

Effort to Defeat Polio Faces Unique Challenges
Unclear When Vaccination Can Be Halted

By David Brown
Washington Post Staff Writer

The troubled 19-year-old campaign to eradicate polio is celebrating recent
progress and an unexpected infusion of cash, but experts are coming to
realize
that they will not be able to end the expensive and laborious efforts to
control
the virus anytime soon.

Ridding the world of polio will be a far messier business than the 1977
eradication of smallpox, which remains a unique achievement in medicine.
That is
because it is now clear that the virus that causes polio could reemerge
years,
and possibly even decades, after the last case is found.

The reason involves peculiarities of poliovirus and the oral (Sabin) vaccine
being used to eradicate the disease.

The vaccine contains a weakened poliovirus that stimulates immunity against
the
"wild" virus, which can cause paralysis. On rare occasions, however, the
vaccine
virus can mutate to a more dangerous form, spread from person to person and
cause a paralytic infection.

This phenomenon, only recognized in the past decade, has caused outbreaks in
10
countries since 2000. This year, 7 percent of all polio cases worldwide were
caused by mutant, vaccine-derived virus.

The only way to prevent this from happening is to keep the world's infants
and
toddlers fully immunized -- in other words, to keep up the exhausting,
expensive
full-court press that has now gone on seven years longer than was
anticipated.

To rid the planet of polio, people will eventually have to stop using the
oral
vaccine. Whether they should forgo immunization altogether or use the
alternative vaccine -- the Salk "polio shot" that does not contain live
virus
and cannot cause infection -- is now under debate.

Switching to the Salk vaccine, however, will be hard.

It's more expensive: roughly $2.70 per dose, compared with 15 cents for the
oral
vaccine. About 135 million infants are born each year, and each will need at
least two shots. While the two companies that make most of the world's
supply
can ramp up production to that level, it will take them at least five years,
and
possibly a lot longer.

Consequently, even after eradication, many countries will have to continue
using
the oral vaccine -- and be prepared to  suppress mini-epidemics caused by
it.

Before the eradication campaign began, polio paralyzed more than 350,000
people
a year in 125 countries. Stopping that suffering is the chief goal of
eradication.

Health officials also hoped the end of polio would also mean the end of
polio
vaccination, with its trouble and expense. That was the case with smallpox.
No
country routinely vaccinates against that disease anymore, a move that has
saved
more than $17 billion in the United States alone.

But an unambiguous transition to a "polio-free" world is unlikely. It will
be
hard to know when, if ever, it is safe to forgo vaccination.

Part of the reason is a fear that terrorists might intentionally reintroduce
the
virus -- a possibility countries did not worry about much when they decided
to
stop smallpox vaccination. But there is also the chance of accidental or
unrecognized release.

Work is underway to identify laboratories holding poliovirus, reduce their
number and increase their security. But unlike with smallpox, there may be
places that have the pathogen and do not know it.

Poliovirus replicates in the intestine. Thousands of labs around the world
have
frozen samples of feces that may contain the virus -- either the wild type
or
the vaccine virus -- that could theoretically escape.

Further complicating matters is the fact that most polio cases are "silent."
In
only 1 in 200 infections from the wild virus is there the characteristic
muscle
weakness that lets physicians make the diagnosis. Polio virus can travel far
before anyone knows it.

The campaign threatened to unravel in 2003 when several populous, largely
Muslim
states of northern Nigeria stopped immunizing because of rumors that the
polio
vaccine contained the AIDS virus or an antifertility drug. The disease
roared back.
By the time vaccination resumed a year later, the virus was out of the barn.

Over the next three years, 20 countries were reinfected with virus traced
via
genetic fingerprinting to strains from northern Nigeria. (Seven other
polio-free
countries were reinfected at the same time after a resurgence of the disease
in
India.) These included not only many African countries but also such faraway
places as Saudi Arabia and Indonesia. Worldwide, polio's annual toll, which
had
fallen to 784 in 2003, climbed to 2,000 last year.

Responding to the Nigerian outbreak took hundreds of millions of dollars and
a
huge amount of work.

The main tool in eradication is National Immunization Day, a coordinated
effort
in which workers go door to door over one or two days and put drops of
vaccine
in the mouths of every child under age 5. Some reinfected countries had to
hold
four or five of these days in a year, rather than just two, to become
polio-free
once more. (Outbreaks caused by vaccine-derived virus are handled the same
way.)

The effort is paying off. The number of reinfected countries is down to
seven,
and the number of countries where the disease is still "endemic," meaning it
has
never been stopped, is now four, the lowest in history. (They are Nigeria,
India, Afghanistan and Pakistan.) Through last Tuesday, only 857 cases of
the
disease had occurred this year.

But in the northern Indian states of Uttar Pradesh and Bihar, which have a
combined population of 270 million, polio is holding on tenaciously.
Astonishingly, one-third of polio cases in northern India last
year were in children who had gotten the vaccine at least 10 times and still
had
not developed immunity.

To address the problem, polio campaigners recently switched to a vaccine
with
only one type of polio virus in it. (Normally, there are three.) This cuts
down
on the competition and targets the specific type of wild virus in the area.
The
campaign is gaining traction.

The initiative, supposed to be completed by 2000, has cost $5.3 billion so
far.
Rotary International, which has 32,000 civic clubs around the world, has
contributed $675 million. Last month, the organization got a $100 million
donation from the Bill and Melinda Gates Foundation, contingent on the
clubs'
matching that sum.
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