The World Health Organization warned Tuesday of large measles outbreaks in countries where immunisation has dropped, after more than 500 cases of the highly contagious disease were reported across Europe in January.
"With steady progress towards elimination over the past two years, it is of particular concern that measles cases are climbing in Europe," the agency's regional director for Europe, Zsuzsanna Jakab, said in a statement.
"Today's travel patterns put no person or country beyond the reach of the measles virus," she said.
The respiratory disease, characterised by high fever and small red spots, usually triggers only mild symptoms, but it remains one of the leading causes of death among young children globally.
Severe complications can occur, however, leading to miscarriage in pregnant women, brain swelling or the risk of death by pneumonia.
The virus is spread by coughing and sneezing, and by close contact with infected individuals. France, Germany, Italy, Romania, Poland, Switzerland and Ukraine were the most affected, accounting for 474 of the 559 cases reported for January.
In these countries, national vaccination levels against the virus are below the 95 percent threshold considered necessary for protecting the entire population.
Preliminary figures for February indicate that the number of new infections is rising sharply, the WHO said.
The figures cover the agency's entire European region, covering 53 countries including Israel, Kazakhstan and Russia. "I urge all endemic countries to take urgent measures to stop transmission of measles within their borders, and all countries that have already achieved this to keep up their guard and sustain high immunisation coverage," Jakab said.