Reuter's med news.

Polio Vaccine a Must, Even After Disease Eradication
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NEW YORK (Reuters Health) Jan 30 - Even if polio is effectively eradicated worldwide, polio immunizations 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. Donald 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 Dr. Henderson, of the Johns Hopkins Center for Civilian Biodefense Studies in Baltimore, Maryland.

Complete polio eradication may prove a difficult feat, Dr. Henderson writes in the January 1st issue of Clinical Infectious Diseases.

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. Although IPV prevents infection, it does not prevent the poliovirus from being shed in the feces--a major concern in countries with poor sanitation.

International health officials have said polio could be eradicated globally by 2005. But Dr. 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 by vaccinated individuals 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.

Dr. 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, Dr. 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.

Clin Infect Dis 2002;34:79-83>>