Progress in the development of poliovirus antiviral agents and their essential role in reducing risks that threaten eradication.

Chronic prolonged excretion of vaccine-derived polioviruses by immunodeficient persons (iVDPV) presents a personal risk of poliomyelitis to the patient as well as a programmatic risk of delayed global eradication. Poliovirus antiviral drugs offer the only mitigation of these risks. Antiviral agents may also have a potential role in the management of accidental exposures and in certain outbreak scenarios. Efforts to discover and develop poliovirus antiviral agents have been ongoing in earnest since the formation in 2007 of the Poliovirus Antivirals Initiative. The most advanced antiviral, pocapavir (V-073), is a capsid inhibitor that has recently demonstrated activity in an oral poliovirus vaccine human challenge model. Additional antiviral candidates with differing mechanisms of action continue to be profiled and evaluated preclinically with the goal of having 2 antivirals available for use in combination to treat iVDPV excreters.

Review and assessment of poliovirus immunity and transmission: synthesis of knowledge gaps and identification of research needs.

With the intensifying global efforts to eradicate wild polioviruses, policymakers face complex decisions related to achieving eradication and managing posteradication risks. These decisions and the expanding use of inactivated poliovirus vaccine (IPV) trigger renewed interest in poliovirus immunity, particularly the role of mucosal immunity in the transmission of polioviruses. Sustained high population immunity to poliovirus transmission represents a key prerequisite to eradication, but poliovirus immunity and transmission remain poorly understood despite decades of studies. In April 2010, the U.S. Centers for Disease Control and Prevention convened an international group of experts on poliovirus immunology and virology to review the literature relevant for modeling poliovirus transmission, develop a consensus about related uncertainties, and identify research needs. This article synthesizes the quantitative assessments and research needs identified during the process. Limitations in the evidence from oral poliovirus vaccine (OPV) challenge studies and other relevant data led to differences in expert assessments, indicating the need for additional data, particularly in several priority areas for research: (1) the ability of IPV-induced immunity to prevent or reduce excretion and affect transmission, (2) the impact of waning immunity on the probability and extent of poliovirus excretion, (3) the relationship between the concentration of poliovirus excreted and infectiousness to others in different settings, and (4) the relative role of fecal-oral versus oropharyngeal transmission. This assessment of current knowledge supports the immediate conduct of additional studies to address the gaps.

Decision analysis in planning for a polio outbreak in the United States.

OBJECTIVE: Global eradication of poliomyelitis may soon be achieved, but circulating polioviruses could reemerge years after eradication by reversion of live attenuated oral vaccine virus to a virulent form, laboratory stock mishandling, or bioterrorism. If a poliomyelitis outbreak occurs in the United States, access to a vaccine stockpile to interrupt viral spread will be necessary. Options for the stockpile include the inactivated polio vaccine and the live-attenuated trivalent and monovalent oral poliovirus vaccines. With differences in immunogenicity, adverse effects, availability, and other issues, the optimal vaccine choice for the stockpile is not clear. We sought to compare vaccine interventions for poliomyelitis outbreak control. DESIGN: We applied decision analysis to 8 strategies for outbreak control: no intervention, 1 or 2 inactivated polio vaccine doses, 1 or 2 trivalent oral poliovirus vaccine doses, 1 or 2 monovalent oral poliovirus vaccine doses, and sequential inactivated polio vaccine-monovalent oral poliovirus vaccine. Historical data from outbreaks in developed countries were used to estimate the risk of paralytic disease after a hypothetical reintroduction of circulating polioviruses. The outcome measure was cases of paralytic poliomyelitis. RESULTS: Monovalent oral poliovirus vaccine provided optimal outbreak control in most scenarios because of high seroconversion rates with 1 dose. Control provided by trivalent oral poliovirus vaccine and inactivated polio vaccine was equivalent at high vaccine coverage rates. At low intervention rates, trivalent oral poliovirus vaccine produced fewer paralytic cases than inactivated polio vaccine in highly immune populations but more cases than inactivated polio vaccine in poorly immunized groups because of secondary transmission of oral poliovirus vaccine virus and vaccine-derived viruses. CONCLUSIONS: This model suggests that monovalent oral poliovirus vaccine would be the most advantageous vaccine for outbreak control. If a monovalent oral poliovirus vaccine stockpile is impractical, the optimal vaccine choice depends on the previous immunity and the anticipated intervention rates.