http://dailynews.yahoo.com/h/nm/20020129/hl/polio_1.html
Tuesday January 29 5:22 PM ET
By Amy Norton
NEW YORK (Reuters Health) - Even if the paralyzing viral infection polio is
effectively eradicated worldwide, polio vaccination should continue, according
to one biodefense expert.
The difficulty of ensuring that polio is indeed wiped out--as well as its
potential use as a biological weapon even after eradication--argue for
continuing vaccination ''indefinitely,'' Dr. D. A. Henderson told Reuters
Health.
At the moment, with polio vaccines still being given throughout the world,
poliovirus does not seem a good choice as a bioweapon. But an end to
vaccination could make the virus ''very attractive'' to aspiring bioterrorists,
according to Henderson, of the Johns Hopkins Center for Civilian Biodefense
Studies in Baltimore, Maryland.
And on the more traditional public health front, truly eradicating polio may
prove a difficult feat, Henderson writes in the January 1st issue of Clinical
Infectious Diseases.
Poliovirus spreads from person to person, and replicates in the body in the
throat and intestines. Most infections go unrecognized because they produce
mild symptoms or none at all. But when the virus attacks nerve cells, it can
lead to paralysis.
The introduction of the inactivated polio vaccine (IPV) in 1955, followed
several years later by the oral polio vaccine (OPV), have sharply cut the
number of polio cases worldwide each year. The last polio case in the US
occurred in 1979.
US children currently receive the IPV, which is injected, because the oral
vaccine, which contains a live, weakened virus, has been found to cause polio
in rare cases. In the developing world, however, the oral vaccine is still used
because it is easier to administer and considered more effective. IPV prevents
a person from becoming ill, but does not prevent poliovirus from being shed in
their feces--a major concern in countries with poor sanitation.
International health officials have said polio could be eradicated globally
by 2005. But Henderson argued that even if this does happen, polio vaccination
should continue.
He pointed to the difficulty of surveillance to ensure that the virus--which
usually does not cause symptoms but is nonetheless transmissible--is indeed
wiped out in developing nations.
In addition, there have been recent small outbreaks of paralytic illness
caused by apparently mutated strains of OPV that had been shed from vaccinated
people and then circulated among others who were not sufficiently protected.
In Hispaniola, which comprises Haiti and the Dominican Republic, a number of
paralytic illnesses among children in 2000 were attributed to an OPV strain
that had reverted to virulence. Such a scenario has also been blamed for a
number of cases in Egypt in the late 1980s and early 1990s.
Henderson noted that the Hispaniola strain was found to have circulated for
2 years before causing any illness. He said that while it appears rare for shed
OPV to mutate, spread and cause illness, these recent reports are a concern in
terms of ending polio vaccination. No one knows, he noted, how long such a
strain could persist silently in the environment and possibly infect the
unvaccinated.
Coupled with the potential of the poliovirus as a bioweapon--or its possible
accidental release from a lab--these factors argue strongly for keeping up
polio vaccination, Henderson stressed.
He said that public health officials are currently debating how to handle
polio once it is considered eradicated. One tactic might be to replace the oral
vaccine with IPV for a while, before eventually stopping polio vaccination.
SOURCE: Clinical Infectious Diseases 2002;34:79-83.
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