Transmission of polio is geographically focal. Operational issues are the main reason children are still being missed by vaccination campaigns, although social and communication problems are also important, particularly in key high-risk areas. Nomadic communities are also at a relatively higher risk of being missed than other groups.
In 2011 Chad was affected by two epidemics: a WPV1 outbreak, which started in N’Djamena in September 2010, and a WPV3 outbreak in the eastern district of Am Dam, which started in November 2007 and re-established transmission. Both were caused by importations from Nigeria. Although the second epidemic is considered to be under control (with no cases detected since March 2011), sub-optimal surveillance warrants caution.
Communication in Action: overview of community engagement.
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.
The publication of the most recent National Emergency Action Plan for Chad covers the period July to December 2012, aims to stop transmission of wild poliovirus by the end of December 2012, and recommends the following emergency approach.
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