With symptoms including high fever and a rash, measles affects 90 percent of those without immunity and is especially unsafe for children under 5 and adults over 20 years old. The World Health Organization (WHO) said this week that a record 41,000 European children and adults have been infected with measles and at least 37 have died in 2018.

Russia has reportedly seen a 13-fold increase in measles cases over the past year as the wider European region grapples with the resurgence of the contagious virus due to fewer vaccinations.

Russia’s Federal Consumer Protection Service, Rospotrebnadzor, has registered 1,717 measles cases between January and June, up by a factor of 13.5 from 127 cases in January-June 2017.

In annual terms, Rospotrebnadzor said there was a 4.5 increase in measles infections from 162 in 2016 to 725 last year. This tracks with WHO’s own yearly figures showing the virus spiking from more than 5,000 cases two years ago to more than 20,000 in 2017.

WHO singled out Russia alongside six other European countries for having more than 1,000 measles infections this year. Ukraine accounted for 23,000 of the 41,000 overall cases, while Serbia outpaced every other country with the highest rate of infections and death numbers.

The watchdog advised Russians on Thursday to get vaccinated at least two weeks ahead of their planned trip to any of the European countries the WHO lists.

Reuters contributed reporting to this article.