poliovirus cases in Africa, supported African regional certification. Modeling of the countries with the last type 3 wild poliovirus cases (i.e., Nigeria, Pakistan and Afghanistan) supported global certification of type 3 wild poliovirus eradication. Sensitivity of monitoring for circulation can be improved by environmental surveillance, which relies on sampling sewage. The availability of environmental surveillance data can shorten the time required to achieve high confidence about no circulation of poliovirus in a population, but this depends on the quality of polio surveillance. References External links Global Polio Eradication Initiative 1995 establishments in Switzerland Medical and health organisations based in Switzerland World Health Organization Organisations based in Geneva