The cause is a combination of complacency, lack of information, opposition to vaccination, distrust of government, and economic and political instability, said Dr. Mark Muscat, a technical officer in the W.H.O.’s immunization program in Europe. There, as in the United States, some people cling to the discredited theory that vaccines can cause autism.
“It’s not just one reason,” Dr. Muscat said. “People are not aware of the potential dangers of this disease, and there are parents who do not see the need to vaccinate their children.”
More than half of this year’s European cases, about 23,000 through June, were recorded in Ukraine, while Italy and Greece have also been unusually hard-hit, with more than 2,000 cases each. In Ukraine, the vaccination rate plunged beginning in 2008, as that country endured political and economic crises, a war against Russian-backed forces and medicine shortages. The rate has rebounded, but there is now a large population of older children who were not immunized.
“You need 95 percent coverage not just at the national level, but in each community, to keep it from spreading,” Dr. Muscat said. He said it was not clear whether the flow into Europe, in recent years, of millions of migrants from the Middle East and Africa, where vaccination rates are lower, had contributed to the increase.
The death rate from measles, which is spread by airborne droplets exhaled by an infected person, is relatively low — a fraction of 1 percent of cases in developed countries, but higher elsewhere — though it can do lasting harm to some survivors. The populations most at risk are people with compromised immune systems who have never had the disease and infants, whose immune systems are not fully developed and who do not receive the first dose of vaccine in the first year after birth.