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The strategies needed to minimize and manage the risks associated with eventual OPV cessation are considered
prerequisites for stopping routine immunization with this vaccine.
Six prerequisites that have been established for OPV cessation.
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Confirmation of interruption and
containment of wild poliovirus transmission
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Continued highly sensitive surveillance for
and rapid notification of poliovirus
circulation
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Establishment of international stockpile of
monovalent oral polio vaccines (mOPV) and global response
mechanism
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Implementation of IPV requirements in
countries that retain poliovirus for research and/or vaccine
production
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International consensus on procedure for synchronous OPV
cessation
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Appropriate bio-containment of Sabin
polioviruses
1. Confirmation of interruption and
containment of wild poliovirus transmission
Issue: Because of the ongoing risk of poliovirus importations into polio-free areas, the interruption
of wild poliovirus transmission must be confirmed in every country in the world prior to the cessation of routine polio immunization anywhere.
All wild polioviruses must be placed under appropriate biocontainment levels on a timely basis to minimize the risk of re-introduction into a polio-free world.
Status of interruption of wild poliovirus: in 1995 the Global Commission for the Certification of Poliomyelitis Eradication (GCC) established the criteria for confirming the interruption of wild poliovirus transmission. As of end-2004, 135 countries in three WHO Regions had been certified polio-free (WHO regions of the Americas, Europe and Western-Pacific).
Next steps for interruption:
Intensified efforts are being made to interrupt the remaining chains of wild poliovirus transmission in the last
four polio-endemic countries and the countries suffering importations
of poliovirus. All countries in regions yet to be certified as polio-free must demonstrate zero polio cases for a minimum of three years, in the presence of 'certification standard' surveillance, prior to OPV cessation.
Status of containment of wild poliovirus:
In 2003, high level biosafety requirements were internationally agreed for vaccine-derived
and wild-type polioviruses. By end-2004, 152 countries had initiated a survey for wild-type and vaccine-derived poliovirus infectious- and potentially-infectious materials, covering over 200,000 facilities. Approximately 850 facilities were identified with relevant infectious-materials. These materials will either be destroyed or placed under appropriate biocontainment conditions.
Next steps for containment: By the time wild poliovirus transmission is interrupted globally, all countries must have completed a national survey and inventory of facilities holding wild or vaccine-derived polioviruses. The process of destroying or properly containing those materials must be completed twelve months later. In
addition, the number of facilities storing, handling and/or
amplifying polioviruses must be reduced to an absolute minimum, in
order to decrease the risk of inadvertent release or
reintroduction into human populations.
Furthermore, these facilities must be
restricted to countries where childhood immunization with the
Inactivated Polio Vaccine (IPV) takes place routinely.
Wild-type polioviruses will have to be substituted with Sabin
viruses in all processes and procedures. A revised edition
of the Global Action Plan for poliovirus containment policy is
currently being finalized.
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2. Continued highly sensitive surveillance for
and rapid notification of poliovirus
circulation
Issue: Highly sensitive surveillance and efficient reporting are required before, during and after OPV cessation to confirm interruption of wild poliovirus transmission, document the elimination of Sabin
strains and rapidly detect the potential reintroduction of any poliovirus.
Status: In 2004, 66 polio-endemic or recently endemic countries met or exceeded the surveillance performance standards established by the
GCC, including most countries that are affected or recovering from conflict such as Afghanistan, Angola, the Democratic Republic of the Congo and Somalia. However, declining rates of acute flaccid paralysis
(AFP) surveillance in a number of countries that have been certified polio-free, and the recent detection in Africa of polioviruses that were missed due to suboptimal AFP surveillance, re-affirms the need to strengthen surveillance and maintain the full certification surveillance criteria everywhere.
Next steps: All countries must strengthen AFP surveillance to ensure it can be sustained at certification standard throughout the three-year plus period of OPV cessation and verification of the elimination of Sabin- and vaccine-derived polioviruses. In addition, high- and middle income countries should screen for
vaccine-derived polioviruses among individuals with primary immunodeficiency
syndromes (iVDPVs). At the international level, event-based reporting for ‘suspect polio’ will need to be fully incorporated into the new International Health Regulations. New diagnostic tools for the OPV cessation phase, particularly IgM assays and direct molecular detection techniques, must be fully evaluated and integrated into the polio laboratory network.
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3. Establishment of international stockpile of
monovalent oral polio vaccines (mOPV) and global response
mechanism
Issue: An international stockpile of types 1, 2 and 3 monovalent OPV is needed particularly to allow a 'type-specific' response during the process of OPV cessation (thereby enhancing the impact of the outbreak response while preventing the reintroduction of other polioviruses).
Status: In 2004, all producers of WHO-prequalified OPV, and their respective national regulatory agencies, were invited to collaborate with WHO on the development, licensure and production of monovalent type 1, type 2 and type 3 OPV. Working estimates have been established for the number of doses required of each mOPV type, development timelines have been elaborated, and the Global Alliance for Vaccines and Immunization
(GAVI) approved a stockpile investment case for funding. As the result of an accelerated vaccine development project,
four mOPV type 1 vaccines and one mOPV3 have been licensed since
early 2005 and are undergoing large-scale field evaluation.
Next steps: The development, production and procurement of mOPV for the stockpile is scheduled to begin in 2006. The mechanisms and criteria for the future use of the stockpile must be completed and internationally-agreed in a World Health Assembly resolution. The potential role of IPV and, possibly antivirals, in outbreak response must also be fully elaborated.
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4. Implementation of IPV requirements in
countries that retain poliovirus for research and/or vaccine
production
Issue: Any country choosing to retain poliovirus (for either
research purposes or in order to produce vaccine) is expected to
have in place a policy of routine IPV immunization which will
ensure coverage sufficient to prevent polio transmission.
Status: To facilitate national decision-making on IPV, WHO in 2004 published an IPV Position Paper summarizing the characteristics, efficacy and potential role of the vaccine. A supplement to this position paper
was published in April 2006 providing additional guidance to
countries on whether to retain poliovirus for scientific purposes
or vaccine production, following OPV cessation, and the
implications of such a policy decision on both biocontainment and
immunization requirements.
A separate WHO study detailed the major programmatic implications of IPV introduction, many of which are not immediately apparent, for most OPV-using countries (e.g. the need to increase cold chain capacity, change the pertussis component of combination vaccines, use vaccines with a different preservative). Initial results from modelling studies commissioned by the Global Polio Eradication Initiative suggest that for most low-income countries, the introduction of IPV for routine immunization would only marginally reduce the already-small risks associated with OPV cessation.
Next steps: Any countries choosing to retain poliovirus must
meet all biocontainment requirements (as per the upcoming Global
Action Plan) and implement routine IPV vaccination activities in
order to achieve and sustain high population immunity against
polio through a coverage rate of at least 90% (with a 4-dose
schedule) and 100% among operators and handlers of polioviruses
and their direct contacts.
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5. International consensus on procedure for synchronous OPV
cessation
Issue: All countries will need to simultaneously stop the use of OPV for routine immunization to ensure that no country is inadvertently put at risk of importing a cVDPV from a country that continues to use OPV.
Status: The international bodies providing oversight to the Global Polio Eradication Initiative have endorsed the need for eventual simultaneous OPV cessation. WHO has begun the process of developing and pilot testing guidelines for the withdrawal of OPV from routine immunization programmes. These guidelines will emphasize the need to maintain the highest-possible level of OPV coverage until the actual time of simultaneous OPV cessation.
Next steps: All remaining polio-infected countries must interrupt wild poliovirus transmission as rapidly as possible to allow the development of a firm timeline for OPV cessation. A World Health Assembly Resolution outlining the precise timing and process for simultaneous OPV cessation by all OPV-using countries could be required as early as
2007. At the national level, detailed plans for the withdrawal and destruction of all trivalent OPV stocks, from all levels of the country, will need to be developed and national immunization policies revised accordingly. Following OPV cessation, documentation of the destruction of remaining trivalent OPV stocks will need to be verified in each country.
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6. Appropriate bio-containment of Sabin
polioviruses
Issue:
Because of their ability to mutate to a virulent form and
re-establish circulation and infection, Sabin polioviruses must be
treated similarly to wild-type polioviruses and placed under
appropriate biocontainment levels.
Status: High-level biosafety requirements have been
agreed on for all types of polioviruses, including Sabin
polioviruses. Guidelines for the specific treatment of Sabin
polioviruses are being developed as part of the revised Global
Action Plan.
Next steps: At an international level, consensus must
be established on appropriate future biosafety containment levels
for Sabin viruses, the timing of the implementation of such
activities and the mechanisms for verification. The development
and licensure of IPV-produced from Sabin strains (SIPV) will
continue to be pursued to further reduce the number of sites
generating high volumes of high titre wild polioviruses for IPV
production.
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