Polio appears in Europe for first time since 2010

Sep 02, 2015, 4:35 PM EDT
In this photograph taken on August 17, 2015, an Afghan health worker administers the polio vaccine to a child during a vaccination campaign on the outskirts of Jalalabad.

The World Health Organization has confirmed two cases of polio in children in the Ukraine resulting in paralyzation. While it looks at the risk of polio spreading across the country, the W.H.O. warns on the lack of vaccinated children. Reports note that 50% of Ukrainian children have been vaccinated against polio, and neither of the two stricken children had been vaccinated. The Washington Post writes:

Poliovirus has returned to Europe after a five year reprieve, paralyzing a 4-year-old and 10-month-old in the Ukraine, the World Health Organization said Wednesday.
The WHO said the two cases were in the southwestern part of the country -- bordering Romania, Hungary, Slovakia and Poland -- and that the strain responsible, vaccine-derived poliovirus type 1 or cVDPV1, may still be a threat to the region.
cVDPV is a rare, mutated form of the virus that comes from the vaccine itself. Oral polio vaccines contain a weakened form of the virus that activates an immune response in the body so that it builds up antibodies to protect itself. But it takes some time for this to happen, and meanwhile the virus replicates in the intestines and can be excreted by the person immunized and can spread to others in the community.
It is likely large numbers of other children have also been infected without developing symptoms.
The WHO said the risk of the virus spreading further in the country was "high" and that the outbreak needed to be rapidly controlled.
One of the paralysed children was four years old and the other just 10 months.
Both were from south-western Ukraine near the border with Romania, Hungary, Slovakia and Poland.
The outbreak started from the weakened form of the virus that is used in vaccination. Sometimes it can mutate and start to spread if immunisation levels are too low.