Between July and September six cases of circulating vaccine-derived poliovirus type 2 (cVDPV2) are reported from Niger, genetically linked to a cVDPV2 in Jigawa and Katsina States, Nigeria. The virus was isolated from children with acute flaccid paralysis (AFP) from Zinder region, located in the south of Niger and on the border with Nigeria, with dates of onset of paralysis ranging from 18 July until 16 of September, according to information available to date. AFP stool samples from Niger were tested at the Senegal laboratory for viral isolation and Intratypic differentiation. Isolates that need to be sequenced were sent to National Institute for Communicable Disease (NICD). Cases have been reported from Tanout, Dungass and Magaria districts.
Nigeria is also reporting a separate cVDPV2 outbreak in Sokoto district since January 2018. Nigeria is one of only three countries in the world classified as endemic for wild poliovirus, along with Afghanistan and Pakistan.
As part of the Lake Chad response, the last monovalent oral polio vaccine type 2 (mOPV2) round was implemented in Niger in January 2017. There is a large cohort lacking immunity against the type-2 poliovirus.
The outbreak response plan is being finalized to include the outbreak zone most at risk and the exact scale and extent of the response is being determined.
The emergence of cVDPV2 in Niger is a reminder that until polio is eradicated, polio-free countries will remain at risk of polio re-infection or re-emergence. The detection of this cVDPV2 strain underscores the importance of maintaining high levels of routine polio vaccination coverage at all levels to minimize the risk and consequences of any poliovirus circulation.
As this outbreak is linked to an ongoing cVDPV2 outbreak in Nigeria, the risk of further international spread associated with this virus remains high.
It is important that all countries, in particular those with frequent travel and contacts with polio-affected countries and areas, strengthen surveillance for AFP in order to rapidly detect any polio case, implement prevention measures, and speed-up the response if needed. Countries should also maintain uniformly on all their territory high polio immunization coverage through routine vaccination to minimize the consequences of any new virus introduction or emergence.
WHO’s International Travel and Health recommends that all travelers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than four weeks) from infected areas should receive an additional dose of oral polio vaccine (OPV) or inactivated polio vaccine (IPV) within four weeks to 12 months of travel. For travelers to Niger, IPV is recommended as it is effective against cVDPV2, whereas the type 2 component is no longer included in OPV.
All countries should report any polio case using the decision instrument in Annex 2 of the International Health Regulations (IHR). Countries affected by polio transmission should comply with the Temporary Recommendations issued by the Director General following advice from the IHR Emergency Committee concerning ongoing events and context involving transmission and international spread of poliovirus. These recommendations include that affected countries declare a national public health emergency, and encourage departing travelers to be vaccinated.