Strategy to eradicate polio in Chad
Context
Conflict in Chad has contributed to a weak health system, low routine immunization coverage and insufficient capacity to fully implement international polio outbreak response guidelines.
These factors have led to circulation of imported wild poliovirus that has persisted for more than 12 months, and the country is classified as having re-established transmission. Furthermore, in 2009, re-established polioviruses in Chad re-infected other, previously polio-free countries and areas.
In Chad, where the re-established virus is still circulating throughout most of the country, the priority is to improve the quality of nationwide campaigns with a combination of monovalent oral polio vaccine type 3 and trivalent oral polio vaccine or bivalent oral polio vaccine, as appropriate to the emerging epidemiology.
Strategic approach in Africa
Compared with Asia, poliovirus transmission persists over a broad area in Africa. In addition, polio outbreaks due to importations generally result in more polio cases over longer periods of time than in Asia. Both are due to weak health systems, resulting in low immunization coverage.
These challenges are off-set by consistently high per-dose efficacy of oral polio vaccine in Africa, and a lower population immunity threshold (80–85%) needed to stop poliovirus transmission.
Consequently, the immunity thresholds needed to stop polio transmission in Africa can be achieved with relatively fewer vaccination campaigns over wide areas and maintaining high coverage.
Strategic approach in Chad
Interrupting the remaining poliovirus transmission in Angola requires the following activities.
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Improving the quality of nationwide campaigns with a combination of monovalent oral polio vaccine type 3 and trivalent oral polio vaccine or bivalent oral polio vaccine, as appropriate to the emerging epidemiology. Particular attention will be given to enhancing the quality of supplementary immunization activities in the capital, N'Djamena, which in 2009 was the primary virus reservoir and where some areas appear to have achieved only 50% supplementary immunization coverage.
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Implementing monovalent oral polio vaccine type 3 mop-up campaigns to supplement the nationwide activities as the virus becomes geographically restricted.
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Enhancing acute flaccid paralysis surveillance to ensure the rapid detection and mop-up of any residual transmission.
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Enhancing resources – particularly international technical assistance and communications – to levels which are comparable to the investment in endemic areas.
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Revising outbreak-response microplans for each area, with refresher training of all key staff.
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Seeking high-level support for terminating outbreaks.
Eradication targets
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End–2010: all re-established wild poliovirus transmission interrupted and <10% missed children in greater N’Djamena and in the southern and eastern poliovirus transmission zones during each supplementary immunization activity in the second half of 2010.
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End–2011: supplementary immunization activity and acute flaccid paralysis surveillance performance of 2010 sustained.
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End–2012: supplementary immunization activity and acute flaccid paralysis surveillance performance of 2010 sustained.