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.

An expert WHO committee said four countries — Albania, the Czech Republic, Greece and the U.K. — have now lost their status as having eliminated measles. Measles is preventable with two doses of the vaccine, but there is no effective treatment once people are infected.

"If high immunization coverage is not achieved and sustained in every community, both children and adults will suffer unnecessarily and some will tragically die," said Dr. Guenter Pfaff, chair of a WHO expert committee on measles in Europe.

In some developed countries, measles vaccination rates dropped sharply following the publication of a flawed study in the late 1990s that linked the combined measles, mumps and rubella vaccine to autism. Health officials have struggled to debunk misperceptions about the vaccine's safety ever since.

"Misinformation about vaccines is as contagious and dangerous as the diseases it helps to spread," WHO Director-General Tedros Adhanom Ghebreyesus in a statement this week.

In 2017, WHO estimated about 110,000 people died from measles worldwide, mostly children under 5-years-old.