Stopping poliovirus vaccination after eradication: issues and challenges

Since 1988 reported polio cases worldwide have declined by about 85% and th e number of known or suspected polio-endemic countries has decreased from o ver 120 to less than 50. With eradication of poliomyelitis approaching, iss ues potentially affecting when and how vaccination against poliovirus can b e stopped become extremely important. Because of the potential risks and be nefits inherent in such a decision, the best available science, a risk-bene fit analysis, contingency plans, a stock pile of poliovirus vaccines, and t he endorsement by the global policy-making committees will all be needed be fore vaccination can be discontinued. The scientific basis for stopping pol io immunization has been reviewed by WHO. This Round Table article summariz es the current state of knowledge, provides an update on the processes and timelines for certification, containment, and slopping vaccination, and hig hlights some of the unanswered scientific questions that will be addressed by further research. These include whether transmission of vaccine-derived poliovirus strains could be sustained so that poliomyelitis could re-emerge in a future unvaccinated population and whether prolonged excretion of vac cine-derived poliovirus from individuals with immune deficiencies could be a mechanism through which this could occur.