outbreaks of paralytic disease. The ability of viruses derived from the oral vaccine to persist in the population poses a substantial challenge to the final stages of eradication.
Another problem is that oral polio vaccination of individuals with immune deficiencies can result in persistent infections, if not disease, in which the vaccine recipient can shed highly neurovirulent virus over extended periods of time. Attempts to cure these individuals have so far been unsuccessful. The known number of persistently infected individuals is exceedingly small, but the actual number of such shedders globally cannot be assessed at the present time.
As long as oral polio vaccine continues to be administered routinely, the spread of vaccine-derived poliovirus is not a problem. Once wild poliovirus is eradicated, an achievement that is anticipated by the global polio eradication campaign authorities in the next few years, the current plan is to discontinue universal administration of oral polio vaccine. Aside from the difficulty of maintaining financial and political support for vaccinating against a virus that seems to have disappeared and is no longer causing disease, the oral vaccine itself causes paralytic disease in a very small number of recipients—about 1-2 per million. At some point, the continued administration of the oral vaccine may pose a greater risk than does the wild virus. As the time approaches when wild poliovirus is expected to be eradicated, a strategy is needed to deal with the ramifications of discontinuing universal vaccination with the oral polio vaccine.
At the request of the Centers for Disease Control and Prevention and the World Health Organization, a committee was established by the National Research Council to organize a workshop to evaluate whether an antiviral drug against poliovirus would be helpful in the final stages of the global polio eradication campaign. The committee was not asked to evaluate the plan to discontinue universal vaccination with oral polio vaccine or other aspects of the post-eradication plans developed by the agencies. Rather, the committee was asked only to address the following issues:
The feasibility and appropriateness of using a polio antiviral drug in the post-eradication era
The properties a polio antiviral compound would need in order to meet the goals of the eradication program
The most promising targets for polio antiviral drug development
A comparison of different approaches to polio antiviral drug development, including an assessment of the required scientific expertise, infrastructural needs, risks, obstacles, and relative costs