Measles cases in the European region surged last year to reach their highest levels since 1997, the World Health Organization and the UN’s children agency, UNICEF, said Thursday.

The number of measles cases in the European region doubled last year to reach the highest level in 25 years, health officials say. A joint report by the World Health Organization (WHO) and the UN children's fund, Unicef, said children under the age of five accounted for more than 40% of the cases reported in Europe and central Asia.

Global organizations have warned that measles cases are now as high as they have been for the past quarter century.