The World Health Organization says the number of measles cases in Europe jumped sharply during the first six months of 2018 and at least 37 people have died.
The U.N. agency's European office said Monday more than 41,000 measles cases were reported in the region during the first half of the year — more than in all 12-month periods so far this decade.
"Following the decade's lowest number of cases in 2016, we are seeing a dramatic increase in infections and extended outbreaks," Zsuzsanna Jakab, WHO regional director for Europe, said in a statement.
The previous highest annual total was 23,927 cases in 2017. A year earlier, only 5,273 cases were reported. In 2017, measles were blamed for 35 deaths in the region.
The agency said half — some 23,000 cases — this year occurred in Ukraine, where an insurgency backed by Russia has been fighting the government for four years in the east in a conflict that has killed over 10,000 people.
France, Georgia, Greece, Italy, Russia and Serbia also had more than 1,000 measles infections each so far this year. Serbia had the highest number of recorded deaths, at 14.
Measles, among the world's most contagious diseases, is a virus that's spread in the air through coughing, sneezing, close personal contact or direct contact with infected nose or throat secretions. The most vulnerable include unvaccinated young children and pregnant women.
It can be prevented with a vaccine that's been in use since the 1960s, but health officials say vaccination rates of at least 95 percent are needed to prevent epidemics.
Vaccine skepticism remains high in many parts of Europe after past immunization problems.
Measles typically begins with a high fever and also causes a rash on the face and neck. While most people who get it recover, measles is one of the leading causes of death among young children, according to the WHO.
Italy has introduced a new law requiring parents to vaccinate their children against measles and nine other childhood diseases. Romania also passed a similar bill, including hefty fines for parents who didn't vaccinate their children.
The U.N. agency on Monday called for better surveillance of the disease and increased immunization rates to prevent measles from becoming endemic.
The Copenhagen-based agency urged the 53 countries in the region to step up immunization efforts. To prevent large outbreaks, it said at least 95 percent immunization coverage is required.
Reasons for the surge included declines in overall routine immunization coverage and low coverage among some marginalized groups.