In a report issued Thursday, the U.N. health agency said the number of measles cases from January to June this year is double the number reported for the same period in 2018. Measles is among the world’s most infectious diseases and is spread mostly by coughing, sneezing and close personal contact.

Although numerous European countries have introduced stronger vaccination policies, stubborn pockets of vaccine refusal have fueled epidemics across the continent. Last month, the German government proposed making measles immunization mandatory for children and employees at kindergartens and schools; there have been more than 400 cases of measles in Germany this year.

With more than 84,000 cases, Ukraine accounted for the vast majority of measles in Europe, followed by Kazakhstan and Georgia. In February, Ukraine’s health ministry said eight people had died of measles.