According to the World Health Organization, two children have been paralyzed in a polio outbreak in the Ukraine, where only half the children are fully immunized.
The who has said that the risk of the disease spreading to other European countries is high and the outbreak needed to be immediately brought under control.
There is no cure for polio, which attacks the nervous system and can cause irreversible paralysis within hours of infection.
A four year old child and ten month old baby are the first to be infected in Europe since 2010.
The outbreak is believed to be started from a weakened form of the virus that is used in vaccinations. The WHO believes it is now a dangerous strain.
The WHO believes that it is likely large numbers of other children have also been infected without developing symptoms, adding, one of the big dangers of the disease is that there are a lot of asymptomatic cases.
The WHO is recommending that everyone visiting the region is fully vaccinated and that all residents and anyone visiting for more than a month get extra doses of polio vaccine.
The two infected children were from south western Ukraine near the border with Romania, Hungary, Slovakia and Poland.