WHO: Circulating vaccine-derived poliovirus type 2 – Niger, Disease Outbreak News (30 October 2018)

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From July through September 2018, six cases of circulating vaccine-derived poliovirus type 2 (cVDPV2) were reported from Niger, genetically linked to a cVDPV2 case 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 through 16 September 2018. This outbreak has also affected Jigawa, Katsina, Yobe, Gombe, and Borno states in Nigeria, with 17 cases reported since April 2018.

Nigeria has also reported a separate cVDPV2 outbreak in Sokoto State that dates back to 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 polio outbreak response in the Lake Chad Basin countries (Cameroon, the Central African Republic, Chad, Niger and Nigeria) the last monovalent oral polio vaccine type 2 (mOPV2) round was implemented in Niger in January 2017.

Public health response

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.

  • Two mOPV2 response vaccination campaigns will reach 3.2 million children under five years of age in four provinces in Niger (Agadez, Diffa, Maradi and Zinder). The first round took place from 24 through 27 October 2018 and the second is scheduled for 7 through 11 November 2018.

  • Acute flaccid paralysis surveillance and routine immunization across the country with focus on the infected provinces and the provinces at the international borders with Nigeria are being reinforced.

  • WHO and its partners are continuing to support local public health authorities in conducting field investigations and risk assessments to more clearly assess risk of the identified cVDPV2 and to conduct additional response measures as appropriate and necessary.

  • Active case finding for additional AFP cases is continuing, and additional surveillance measures such as increasing the frequency and extent of environmental surveillance and community sampling of healthy individuals is being expanded.

  • WHO is supporting the Ministry of Health to strengthen the risk communication and community engagement.

  • WHO in collaboration with the Ministry of Health are working together to finalize the deployment of the human resources needed at national and provincial levels.

WHO risk assessment

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.

WHO advice

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 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 travellers 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 travellers 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 travellers to be vaccinated.