Global health officials are reporting the confirmation of two cases of circulating vaccine-derived poliovirus type 1 (cVDPV1)  in south-western Ukraine. The cases, ages 4 years old and 10 months old have onset of paralysis on 30 June and 7 July 2015.

Poliovirus  Image/CDC
Poliovirus Image/CDC

The World Health Organization (WHO) says Ukraine had been at particular risk of emergence of a cVDPV, due to inadequate vaccination coverage. In 2014, only 50% of children were fully immunized against polio and other vaccine-preventable diseases.

What are Circulating vaccine-derived poliovirus (cVDPV)?

The Global Polio Eradication Initiative defines it as follows:

On very rare occasions, if a population is seriously under-immunized, there are enough susceptible children for the excreted vaccine-derived polioviruses to begin circulating in the community. These viruses are called circulating vaccine-derived polioviruses (cVDPV).

The lower the population immunity, the longer these viruses survive. The longer they survive, the more they replicate, change, and exchange genetic material with other enteroviruses as they spread through a community. If a population is fully immunized against polio, it will be protected against the spread of both wild and vaccine strains of poliovirus.

An emergency outbreak response is being planned  that will include  a minimum of three large-scale supplementary immunization activities with an appropriate oral polio vaccine, to begin within two weeks of confirmation of the outbreak and covering a target population of 2 million children aged less than five years, and the public declaration of the outbreak as a national public health emergency.

WHO currently assesses the risk of international spread from Ukraine to be low, but notes that the infected oblast (Zakarpatskaya) shares borders with four countries (Romania, Hungary, Slovakia and Poland).

WHO recommends that all travelers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of oral polio vaccine (OPV) or inactivated polio vaccine (IPV) within 4 weeks to 12 months of travel.

Robert Herriman is a microbiologist and the Editor-in-Chief of Outbreak News Today

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